Trivalent chromium plating film, trivalent chromium plating product, and method for producing trivalent chromium plating product

Abstract

A trivalent chromium plating product according to the present disclosure is obtained by a trivalent chromium plating treatment. The color difference ΔE of the plating film of the trivalent chromium plating product from a hexavalent chromium plating film is less than 3.5.

Description

Trivalent chromium plating film, trivalent chromium plating product, and method for manufacturing trivalent chromium plating product

[0001] The present disclosure relates to a trivalent chromium plating film, a trivalent chromium plating product, and a method for manufacturing a trivalent chromium plating product. This application claims priority based on Japanese Patent Application Nos. 2024-125112 and 2024-125136, filed on July 31, 2024, the contents of which are incorporated herein by reference.

[0002] Chrome plating imparts a silvery luster and offers excellent corrosion resistance, making hexavalent chromium plating solutions widely used in the metal finishing industry for both decorative and hard chromium plating. However, in recent years, environmental considerations have led to the development of plating solutions containing trivalent chromium, which do not contain hexavalent chromium. However, it has generally been difficult to achieve the same performance as hexavalent chromium plating with plating solutions containing trivalent chromium. For example, trivalent chromium electrolytes tend to be more sensitive to metal impurities than hexavalent chromium electrolytes. Furthermore, the color of trivalent chromium coatings is darker than that of hexavalent chromium coatings.

[0003] In recent years, various trivalent chromium plating solutions have been reported that aim to achieve the same performance as hexavalent chromium plating. For example, a method for improving the corrosion resistance of a trivalent chromium coating (Patent Document 1) and a method for controlling the color of a trivalent chromium coating (Patent Document 2) have been reported.

[0004] Special table No. 2021-507114 Publication No. 2015-510549

[0005] The above-mentioned trivalent chromium plating, particularly decorative trivalent chromium plating, has a problem in that it is not possible to obtain a coating having the same glossy appearance as hexavalent chromium plating.

[0006] The present disclosure has been made in view of the above circumstances, and provides a trivalent chromium plating film having a glossy appearance equivalent to that of hexavalent chromium plating, a trivalent chromium plating product, and a method for manufacturing a trivalent chromium plating product.

[0007] As a result of extensive research, the present inventors have found that the above-mentioned problems can be solved by using a specific trivalent chromium plating solution, plating conditions, etc., and have completed the present invention.

[0008] Furthermore, as a result of extensive research, the present inventors have discovered that the above-mentioned problems can be solved by using a trivalent chromium plating coating having a nanostructure with an average crystal grain size (D) of 30 nm or more and 180 nm or less, and have completed the invention.

[0009] That is, the present disclosure encompasses the following aspects. [1] A trivalent chromium plating product, wherein the plating film of the trivalent chromium plating product has a color difference ΔE from a hexavalent chromium plating film of less than 3.5. [2] The trivalent chromium plating product according to [1], wherein the plating film of the trivalent chromium plating product has a color difference ΔE from a hexavalent chromium plating film of less than 2.0. [3] The trivalent chromium plating product according to [1] or [2], wherein the plating film of the trivalent chromium plating product has a lightness difference ΔL value from a hexavalent chromium plating film of less than 2.0, and wherein the color characteristics are an a-value of +2.0 to -2.0 and a b-value of +2.0 to -2.0. [4] The trivalent chromium plating product according to any of [1] to [3], wherein the thickness of the plating film of the trivalent chromium plating product is 1 μm or less. [5] The trivalent chromium plating product according to [4], wherein the thickness of the plating film of the trivalent chromium plating product is 0.05 μm or more and 0.4 μm or less. [6] The trivalent chromium plating product according to any one of [1] to [5], wherein the plating film of the trivalent chromium plating product has an L value of 65 to 90, a lightness difference ΔL value of less than 2.0, an a value of +0.5 to -1.0, and a b value of +1.0 to -1.5. [7] A trivalent chromium plating product obtained by a method for producing a trivalent chromium plating product, the method for producing a trivalent chromium plating product comprising a plating treatment step of passing a current through a trivalent chromium plating solution using an object to be plated as a cathode, the trivalent chromium plating solution comprising a Cr supply source and a complexing agent, the Cr supply source being at least one selected from the group consisting of chromium compounds of sulfuric acid, basic sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, and the complexing agent comprising at least one or more organic acids selected from the group consisting of saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, and carboxylic acid derivatives. The trivalent chromium plating product according to any one of [1] to [6].[8] A trivalent chromium plated product according to any one of [1] to [6], obtained by a method for producing a trivalent chromium plated product, the method comprising: a plating step of passing a current through a trivalent chromium plating solution using a substrate as a cathode to obtain a plated product; and a post-treatment step of electrolyzing or acid-immersing the substrate obtained in the plating step. [9] A trivalent chromium plated product according to any one of [1] to [6], obtained by a method for producing a trivalent chromium plated product, the method comprising: a plating step of passing a current through a trivalent chromium plating solution using a substrate as a cathode to obtain a plated product; and an ion-removal step of removing ions of metals other than Cr, the ion-removal step using an ion-exchange resin to remove ions of metals other than Cr.

[10] A trivalent chromium plating film having a nanostructure with an average crystal grain size (D) of 30 nm or more and 180 nm or less. The method for evaluating the average crystal grain size (D) includes the steps of: using a scanning electron microscope (SEM) to set one or more random test lines on the surface of the plating film; and calculating the average crystal grain size by averaging the sum of the lengths of individual grains (nanostructures) intersecting the test line by the quotient of the number of measured grains.

[11] The trivalent chromium plating film according to

[10] , which has a nanostructure with an average crystal grain size (D) of 50 nm or more and 120 nm or less.

[12] The trivalent chromium plating film according to

[10] or

[11] , which is obtained by post-treating the surface of the trivalent chromium plating film with acid.

[13] The trivalent chromium plating film according to any one of

[10] to

[12] , which has a plating thickness of 0.05 μm or more.

[14] The trivalent chromium plating film according to any one of

[10] to

[13] , which has an R.N. of 9.0 or more according to the CASS test method. The CASS test method is described in Japanese Industrial Standards (JIS) Z 2371, and is a method for evaluating the corrosion state after a test time of 24 hours. RN 10 means a corrosion area ratio of 0.00%, RN 9 means a corrosion area ratio of 0.10%, and RN 9.0 or higher means a corrosion area ratio of 0.10% or less.

[15] A trivalent chromium plating product having the trivalent chromium plating coating according to any one of

[10] to

[14] .

[16] A method for producing a trivalent chromium plated product, comprising a plating treatment step of passing a current through a substrate as a cathode in a trivalent chromium plating solution, wherein the trivalent chromium plating solution comprises a Cr source and a complexing agent, the Cr source comprises at least one selected from the group consisting of chromium compounds of sulfuric acid, basic sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, the complexing agent comprises at least one selected from the group consisting of saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, and carboxylic acid derivatives, and the plating film of the trivalent chromium plated product has a color difference ΔE of less than 3.5 from a hexavalent chromium plating film.

[17] The method for producing a trivalent chromium plated product according to

[16] , wherein the plating film of the trivalent chromium plated product has a lightness difference ΔL value from a hexavalent chromium plated film of less than 2.0, and color characteristics of which are an a value of +2.0 to -2.0 and a b value of +2.0 to -2.0.

[18] The method for producing a trivalent chromium plated product according to either

[16] or

[17] , wherein the plating film of the trivalent chromium plated product has a thickness of 0.2 μm or more and 1 μm or less.

[19] The method for producing a trivalent chromium plated product according to any one of

[16] to

[18] , wherein the Cr source is not a chromium compound selected from hydrochloric acid, nitric acid, and phosphoric acid, the Cr source contains chromium (III) sulfate or basic chromium (III) sulfate, and the chromium (III) sulfate or basic chromium (III) sulfate concentration is 0.4 to 0.6 mol / L, and the complexing agent contains saccharin, oxalic acid, or formic acid, and the molar ratio of the total of saccharin, oxalic acid, and formic acid to Cr is 1 / 2 to 1 / 20.

[20] In the plating step, the plating temperature is 30 to 65°C, the plating pH is 2.8 to 4.2, and the plating current density is 3 to 10 A / dm. ２

[21] The method for producing a trivalent chromium plated product according to any one of

[16] to

[19] , wherein the plating electrode is one or more selected from the group consisting of Ti, Pt, Ir oxide, and Ta.

[21] In the plating step, the plating time is 3 to 30 minutes, the plating efficiency is 0.1 to 10%, the electrode distance is 200 to 500 mm, and the stirring speed is 5 to 500 L / min m ２

[22] The method for producing a trivalent chromium plated product according to any one of

[16] to

[20] , wherein the plating electrode uses one or more selected from the group consisting of Ti, Pt, Ir oxide, and Ta.

[22] In the plating step, the plating temperature is 50 to 56°C, the plating pH is 3.0 to 3.8, and the plating current density is 5 to 8 A / dm ２ ) The plating treatment time is 3 to 10 minutes, the plating treatment electrode distance is 250 to 350 mm, and the plating treatment stirring speed is 7 to 54 L / min·m ２ The method for producing a trivalent chromium plating product according to any one of

[16] to

[21] .

[0010] FIG. 1 is a diagram illustrating the principle of a trivalent chromium plating apparatus according to the first embodiment. FIG. 2 is a diagram illustrating the relationship between the electrode distance and the width of the workpiece to be plated according to the first embodiment (when the workpiece is narrow). FIG. 3 is a diagram illustrating the relationship between the electrode distance and the width of the workpiece to be plated according to the first embodiment (when the workpiece is wide). FIG. 4 is a diagram illustrating the principle of an evaluation method for the throwing power of a chromium plating product (when the throwing power is good). FIG. 5 is a diagram illustrating the principle of an evaluation method for the throwing power of a chromium plating product (when the throwing power is insufficient). FIG. 6 is a diagram illustrating the relationship between the concentration of various ions other than Cr and the immersion volume when trivalent chromium plating is performed for 8 minutes and then repeatedly immersed in the solution for 40 minutes in Comparative Example C1, when an ion removal step for removing ions of metals other than Cr using an ion exchange resin is not included. FIG. 7 is a diagram illustrating the relationship between the amount of untreated solution and elapsed time when 120 L of plating solution is passed through the ion exchange resin at a circulation rate of 2 L / min in Reference Example C1, when an ion removal step for removing ions of metals other than Cr using an ion exchange resin is included. FIG. 8 is a graph showing the relationship between the concentrations of various ions other than Cr and the elapsed time when 120 L of plating solution was passed through the ion exchange resin at a circulation rate of 2 L / min in Reference Example C1, in which an ion removal step of removing ions of metals other than Cr using an ion exchange resin was included.

[0011] FIG. 9 is a scanning electron microscope (SEM) image of the trivalent chromium plating film produced in Example D1. FIG. 10 is a scanning electron microscope (SEM) image of the trivalent chromium plating film produced in Example D2. FIG. 11 is a scanning electron microscope (SEM) image of the trivalent chromium plating film produced in Example D3. FIG. 12 is a scanning electron microscope (SEM) image of the trivalent chromium plating film produced in Example D4. FIG. 13 is a scanning electron microscope (SEM) image of the trivalent chromium plating film produced in Example D5. FIG. 14 is a scanning electron microscope (SEM) image of the trivalent chromium plating film produced in Example D6. FIG. 15 is a scanning electron microscope (SEM) image of the hexavalent chromium plating film produced in Comparative Example D1. FIG. 16 is a principle diagram showing a corrosion model of a trivalent chromium plating film.

[0012] The following embodiment shows one aspect of the present disclosure, does not limit the present disclosure, and can be modified as desired within the scope of the technical idea of ​​the present disclosure. In the following drawings, the scale of each structure is different from the actual structure to make each configuration easier to understand.

[0013] (Trivalent Chromium Plated Product) The trivalent chromium plated product of one embodiment of the present disclosure is a trivalent chromium plated product treated with trivalent chromium plating. The plating film of the trivalent chromium plated product of this embodiment has a color difference ΔE from a hexavalent chromium plated film of less than 3.5. The plating film of the trivalent chromium plated product of this embodiment preferably has a color difference ΔE from a hexavalent chromium plated film of less than 2.0. The trivalent chromium plated product of this embodiment has excellent plating film appearance, and the color difference ΔE from a hexavalent chromium plated film, which is a thin metal film electrolytically generated from an aqueous solution of chromic acid and sulfuric acid, is not noticeable even when mixed with a hexavalent chromium product. In the present disclosure, the "trivalent chromium plated product" refers to a plated object treated with trivalent chromium plating. The plated product includes a plated object and a trivalent chromium plated film covering part or all of the plated object. Examples of the plated object include parts and products used in household appliances, such as faucet spouts, spout pipes, stop valves, and handles, as well as handles for cabinets and doors. A "trivalent chromium plating film" is a chromium metal film formed by electrolytic reduction of trivalent chromium ions. That is, it is a chromium metal film derived from trivalent chromium ions. A "hexavalent chromium plating film" is a chromium metal film formed by electrolytic reduction of hexavalent chromium ions. That is, it is a chromium metal film derived from hexavalent chromium ions. Theoretically, trivalent chromium plating films and hexavalent chromium plating films are the same chromium metal film, but due to the difference in the valence of the derived chromium ions, it is presumed that the metal microstructures, trace amounts of components other than chromium, and mechanical properties of the metal films differ. Furthermore, the type of derived chromium ions also tends to be labeled on the final product. Therefore, it is recognized that "trivalent chromium plating films" and "hexavalent chromium plating films" are films with different properties.

[0014] The plating film of the trivalent chromium plating product preferably has a lightness difference ΔL value from the hexavalent chromium plating film of less than 2.0, more preferably ΔL of 1.5 or less. The lightness difference ΔL may be 0.1 or more, 0.2 or more, 0.5 or more, or even 1.0 or more. The lightness difference ΔL value is the absolute value of the difference between the lightness L of the plating film of the trivalent chromium plating product obtained using a substrate (substrate) having the same uneven shape and the lightness L of the plating film of the hexavalent chromium plating product. The plating film of the trivalent chromium plating product more preferably has a color characteristic a value of +2.0 to -2.0 and a b value of +2.0 to -2.0. From the viewpoint of ensuring an excellent appearance, the thickness is preferably 0.2 μm or more. Furthermore, from the viewpoint of cost-effectiveness of decorative chromium plating products, the thickness of the plating film may be 1 μm or less. The thickness is preferably 0.05 μm or more and 0.8 μm or less, and even more preferably 0.05 μm or more and 0.4 μm or less. The plating film of the trivalent chromium plating product of this embodiment preferably has an R.N. of 9.0 or more, more preferably an R.N. of 9.3 or more, and even more preferably an R.N. of 9.5 or more, in the CASS test described below.

[0015] The trivalent chromium plating product of this embodiment is not particularly limited by its manufacturing method as long as it has the above-mentioned color characteristics, but is preferably obtained by the manufacturing method of a trivalent chromium plating product described below. As described above, the trivalent chromium plating product of this embodiment can be evaluated to a certain extent based on color characteristics, etc., but there are still many unknowns regarding the relationship between the microstructural characteristics of the resulting product and the above-mentioned color characteristics, which depend on the components of the trivalent chromium plating solution, plating conditions, etc. Microstructural characteristics include, for example, components other than Cr metal in the coating, surface microstructure, cross-sectional microstructure, and metallic chromium structure. The relationship between these characteristics and the above-mentioned color characteristics, etc., is still largely unknown. In particular, the comparison of the microstructures of metallic chromium coatings obtained by trivalent chromium plating and hexavalent chromium plating has not been fully elucidated. The evaluation of the trivalent chromium plating product, the manufacturing method of the trivalent chromium plating product, and the hexavalent chromium plating coating and its manufacturing method are described in detail below.

[0016] [Evaluation of Trivalent Chromium Plating Product Coating] [Color Difference ΔE] When the colors of the reference hexavalent chromium plating are L6, a6, and b6, and the colors of the trivalent chromium plating are L3, a3, and b3, the color difference ΔE can be calculated using the following formula. The method for measuring the color difference will be explained in the examples.

[0017] ΔE=√((L6-L3) ２ + (a6-a3) ２ + (b6-b3) ２ )

[0018] For example, if the differences in L are 2, a is 2, and b is 2, then ΔE = √(4 + 4 + 4) = √12 = 3.46. The plating solution and plating conditions used for the reference hexavalent chromium plating will be described later. The substrate (subject to be plated) for the hexavalent chromium plating may have the same uneven shape as the trivalent chromium plating to be compared, or may be the same substrate as the trivalent chromium plating to be compared. In this case, the above value (L6 - L3) can exclude the influence of reflectivity, which changes due to the unevenness of the substrate.

[0019] [Lightness Difference ΔL Value] The appearance of a trivalent chromium-plated object can be expressed by the a-value, b-value, and L-value. Here, the L-value refers to lightness, and is also affected by the substrate. Therefore, a more accurate representation of the color tone of the plating itself can be achieved by using the lightness difference ΔL, which excludes the influence of reflectance that varies with substrate unevenness. That is, using substrates with the same uneven shape, hexavalent chromium plating and trivalent chromium plating are performed, respectively. The absolute value ΔL of the difference between the lightness L6 of the resulting hexavalent chromium plating film and the lightness L3 of the trivalent chromium plating film (L3 - L6) can be used to indicate the range required for plating. For example, for a stop valve with a rough surface, the conventional hexavalent chromium plating film has an L6 of 72.85, while the trivalent chromium plating film of this embodiment has an L3 of 72.50. For a spout with a fine surface, the hexavalent chromium plating film has an L6 of 86.68, and the trivalent chromium plating film has an L3 of 87.07. The L value indicates brightness and changes with reflectance, so it is affected by the unevenness of the substrate. As a result, even with the same plating, the L6 values ​​for a stopcock with a rough surface and a spout with a fine surface are significantly different, at 72.85 and 86.68, respectively. In other words, the L value can also be considered to represent appearance. On the other hand, when comparing the same substrate as described above, because the substrate has the same uneven shape, the brightness difference between hexavalent chromium and trivalent chromium, expressed as ΔL, is 0.35 for the stopcock and 0.39 for the spout, so there is almost no difference. By clarifying the standard, the color difference in the plating can be accurately captured. The above-mentioned deliverables are intended to be plumbing fixtures such as spouts, spout pipes, stopcocks, and handles, but the same can also be applied to parts and products used in residential equipment, not just plumbing fixtures.

[0020] [Method for Producing Trivalent Chromium Plated Product] Examples of the method for producing the trivalent chromium plated product of this embodiment include the following manufacturing methods of the first embodiment, second embodiment, and third embodiment.

[0021] <First embodiment> A method for producing a trivalent chromium plated product of this embodiment includes a plating treatment step of passing an electric current through a trivalent chromium plating solution, with the substrate being used as a cathode. The trivalent chromium plated product obtained by this method for producing a trivalent chromium plated product of this embodiment has a color difference ΔE of less than 3.5 compared to a conventional hexavalent chromium plating film, so that the trivalent chromium plated product does not become a problem even if it is mixed with a hexavalent chromium product, and it is easier to gradually convert from a conventional hexavalent chromium plating method to a trivalent chromium plating method.

[0022] FIG. 1 shows a principle diagram of a trivalent chromium plating apparatus according to this embodiment. In the plating process, for example, as shown in FIG. 1 , a workpiece 1 is immersed between two anodes (2A, 2B) in a trivalent chromium plating solution 4 in a plating tank 5. Then, a current is passed through the workpiece 1, which serves as the cathode 3, to plate the workpiece. That is, a metal chromium plating is formed from a chemical containing trivalent chromium as a primary component. An anode chamber (not shown) may be formed near the anodes (2A, 2B), for example, using a known cation exchange membrane. Examples of the anodes (2A, 2B) include Ti electrodes coated with a known thin film of Ir—Ta composite oxide. The cathode 3 is electrically connected to the workpiece 1. If necessary, an agitator (not shown) for agitating the trivalent chromium plating solution 4 may also be provided.

[0023] In addition to the above plating process, the method for producing a trivalent chromium-plated product of this embodiment may include, as necessary, a pretreatment process for cleaning, a nickel plating process, and a post-treatment process including cleaning.

[0024] The pretreatment process for the purpose of cleaning includes dissolving metal surfaces and processing oils that have oxidized over time, alkaline removal of machining oils, ultrasonic cleaning of processing and polishing residues, physical foaming cleaning by electrolysis in alkali, chemical dissolution cleaning, and acid neutralization of alkaline cleaning solutions. By appropriately combining these processes, the substrate can be made more suitable for plating. Note that, in the embodiments of the present disclosure, a pretreatment process is not necessarily required. Furthermore, while examples of pretreatment processes have been described above, they are not limited to the above, and can be appropriately selected and combined as needed, and the order is not limited.

[0025] The nickel plating process is a process of plating nickel. For example, seal nickel, bright nickel, supplemental flash nickel, semi-bright nickel, electroless nickel, emulsion nickel, etc. are used. This process allows the surface to be chrome-plated or the surface after chrome plating to have the desired unevenness. It is desirable to use a nickel plating that is suited to the substrate, application, and purpose of the object to be plated.

[0026] The post-treatment including cleaning is, for example, a post-treatment of the plated object obtained in the plating process by electrolysis or acid immersion. The electrolysis method is a method of forming a protective coating on the surface of the plated object using electrolysis. The acid immersion method is a method of immersing the plated object in an acidic solution to form a protective coating on the surface or passivate the plated object. This can further stabilize the surface of the coating.

[0027] Although four main steps have been described above, it is also possible to perform the plating process on the object to be plated by repeating the described processes multiple times, and by adding processes as needed, such as a water rinse process, between each process.

[0028] [Substrate to be Plated] Substrates to be plated include materials such as iron substrates (e.g., non-ferrous copper alloys, zinc, zinc alloys, and stainless steel) and resin substrates. For example, when a copper alloy substrate is used, nickel plating is applied to the substrate, followed by chrome plating as the outermost layer. When zinc or a zinc alloy substrate is used, copper plating is applied to the substrate, followed by nickel plating, and then chrome plating as the outermost layer. When a resin substrate is used, the substrate is subjected to a conductive treatment such as electroless plating of copper or nickel, followed by semi-bright nickel and bright nickel plating, followed by chrome plating as the outermost layer. This layered structure, excluding surface treatments, in which chrome plating is applied as the outermost layer, i.e., nickel plating or alloy plating, can create the desired unevenness on the surface to be chrome-plated or the surface after chrome plating. The substrate to be plated in this embodiment may also be an object that has already been treated with the nickel plating process described above. For example, when the substrate of the object to be plated is a copper alloy substrate, a zinc or zinc alloy substrate, or a resin substrate, the substrate may be treated with the above-mentioned nickel plating, the above-mentioned copper plating / nickel plating, or the above-mentioned copper or nickel electroless plating / nickel plating.

[0029] [Trivalent chromium plating solution] The trivalent chromium plating solution according to this embodiment contains a Cr source, a complexing agent, an auxiliary complexing agent, an auxiliary agent, a pH buffer, a conductive salt, and a surfactant. An example of a commercially available plating solution is SurTec 883XT (manufactured by SurTec MMC Japan Co., Ltd.).

[0030] <Cr Source> Examples of the Cr source include chromium compounds of sulfuric acid, basic sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. The Cr source is preferably a sulfate-based compound, which is less likely to unintentionally incorporate unnecessary substances into the coating. Chromium (III) sulfate or basic chromium (III) sulfate is particularly preferred. The content of the Cr source in the trivalent chromium plating solution is not particularly limited, but is preferably 0.3 to 1.0 mol / L, and more preferably 0.4 to 0.6 mol / L, in terms of Cr ions.

[0031] <Complexing Agent> Examples of the complexing agent include organic acids selected from the group consisting of carboxylic acids such as saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, and amino acids, or derivatives of such organic acids. One or more complexing agents can be appropriately selected and combined for use. Examples of the organic acid derivatives include amides such as saccharin, and sodium, potassium, and ammonium salts of the carboxylic acids. Specific examples of the organic acids include acetic acid, oxalic acid, formic acid, succinic acid, lactic acid, maleic acid, malonic acid, malic acid, carboxylic acids, tricarboxylic acids, aminocarboxylic acids, tartaric acid, and glycine. The complexing agent is preferably saccharin, which is difficult to incorporate into the coating, oxalic acid with a small molecular weight, or formic acid. Saccharin is more preferred. For example, when obtaining a trivalent chromium coating, it is necessary to add a complexing agent to the plating solution to facilitate chromium deposition. However, organic matter is incorporated into the chromium coating, resulting in a lower purity and darker color than a hexavalent chromium coating. Complexing agents have the effect of lowering the high deposition potential of trivalent chromium ions. In other words, the inclusion of such agents results in chromium deposition relative to the predominant water electrolysis, resulting in the deposition of chromium ions. Specifically, chromium deposition can be made more prevalent than water electrolysis, thereby promoting the deposition of chromium ions. Specifically, trivalent chromium ions have a more positive potential than hexavalent chromium ions, and even if the energy is increased, water electrolysis prevails and chromium deposition does not occur. Therefore, when depositing trivalent chromium ions, the potential can be controlled to facilitate deposition by complex formation. The content of the complexing agent in the trivalent chromium plating solution is not particularly limited, but a molar ratio of the complexing agent to Cr of 1 / 1 to 1 / 26 is preferred. The content of the complexing agent in the trivalent chromium plating solution is not particularly limited, but is preferably 0.02 to 0.07 mol / L, and more preferably 0.03 to 0.05 mol / L, for example.

[0032] <Auxiliary Agents> Auxiliary agents are added to adjust various properties of the plating solution. Their functions are diverse, including improving corrosion resistance, assisting complex formation, adjusting color, extending the life of the plating solution, and adjusting efficiency. Examples of the auxiliary agent include organic compounds, inorganic acids, and alcohols. More specific examples include sodium thiocyanate, ascorbic acid, sodium ascorbate, hydrogen peroxide, polyethylene glycol, tin salts such as tin sulfate and tin chloride, iron chloride, iron sulfate, sodium allylsulfonate, vinylsulfonic acid, and thiourea. One or more auxiliary agents can be appropriately selected and combined for use. The amount of the auxiliary agent added to the trivalent chromium plating solution is not particularly limited and may be adjusted depending on the plating state of the finished product.

[0033] <pH Buffer> Examples of the pH buffer include boric acid and salts of boric acid. Boric acid acts to buffer the pH of the product surface from shifting to alkaline during plating. However, depending on the concentration, it has the tendency to crystallize at low temperatures. By adjusting the content to an appropriate level, a good appearance can be obtained. The content of the pH buffer in the trivalent chromium plating solution is not particularly limited, but is preferably 40 to 100 g / L, and more preferably 70 to 90 g / L, for example.

[0034] <Conductive Salt> Examples of the conductive salt include compounds of sulfuric acid, hydrochloric acid, and nitric acid with sodium, potassium, and ammonium. The conductive salt influences the liquid junction resistance of the plating solution. A good appearance can be obtained by adjusting the content appropriately. If the amount is insufficient, the liquid junction resistance increases. However, since there is a limit to the amount that can be dissolved, the content must be adjusted appropriately. The content of the conductive salt in the trivalent chromium plating solution is not particularly limited, but is preferably a sulfate-based salt of the same type as the anion used in the Cr supply source. For example, the content of sodium sulfate is preferably 100 to 250 g / L, more preferably 150 to 230 g / L.

[0035] <Surfactant> Examples of the surfactant include succinic acid, sulfosuccinic acid, alkylsulfosuccinic acid, dodecylbenzenesulfonic acid, and alcohols. The surfactant serves to increase the affinity between the metal plating surface and the solution, thereby maintaining adhesion strength. The content of the surfactant in the trivalent chromium plating solution is not particularly limited, but is preferably 0.03 to 0.90 g / L, and more preferably 0.05 to 0.18 g / L, of alkylsulfosuccinic acid, for example.

[0036] [Trivalent chromium plating conditions] The method for producing a trivalent chromium plated product of this embodiment may perform a plating process in which an electric current is applied to the substrate as the cathode under the following plating conditions. Examples of the plating conditions include the plating temperature, plating pH, plating time, plating efficiency, plating electrode distance, plating stirring speed, and plating electrodes. A good trivalent chromium plated product can be obtained by using one or a combination of two or more of these conditions.

[0037] The plating temperature is the temperature of the plating solution. The plating temperature is, for example, preferably 30 to 65° C., and more preferably 50 to 56° C. Within this temperature range, crystallization of boric acid does not occur, and a glossy appearance can be obtained.

[0038] The plating treatment pH is the pH of the plating solution. The plating treatment pH is preferably 2.8 to 4.2, and more preferably 3.0 to 3.8. Within this pH range, a good trivalent chromium plating product can be obtained, in which complex formation with Cr occurs.

[0039] The plating treatment current density is 4 to 10 A / dm ２ is preferable, and more preferably 5 to 8 A / dm ２ In this range, hexavalent Cr ions are not formed.

[0040] The plating treatment time is the time for which current is applied. The plating treatment time is preferably 3 to 30 minutes, more preferably 5 to 10 minutes. Within this treatment time range, a better color tone can be obtained. The plating treatment electrode distance is preferably 200 to 500 mm, more preferably 250 to 350 mm. The plating treatment stirring speed is the speed at which the solution is stirred. The plating treatment stirring speed is 5 to 100 L / min·m ２ is preferable, and more preferably 7 to 54 L / min m ２ The plating electrode preferably uses at least one material selected from the group consisting of Ti, Pt, Ir oxide, and Ta.

[0041] "Implementation of the Manufacturing Method of the First Embodiment" Specific implementations of the manufacturing method of the first embodiment include, for example, the following [A1] to [A5]. [A1] A manufacturing method for manufacturing a trivalent chromium plated product, comprising a plating treatment step of passing a current through a substrate to be plated as a cathode in a trivalent chromium plating solution, wherein the trivalent chromium plating solution contains a Cr source and a complexing agent, the Cr source is at least one selected from the group consisting of chromium compounds of sulfuric acid, basic sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid, and the complexing agent contains at least one organic acid selected from the group consisting of saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, and carboxylic acid derivatives. [A2] The method for producing a trivalent chromium plated product according to [A1], wherein the Cr source is not a chromium compound such as hydrochloric acid, nitric acid, or phosphoric acid, the Cr source contains chromium sulfate (III) or basic chromium sulfate (III), and the concentration of the chromium sulfate (III) or basic chromium sulfate (III) is 0.4 to 0.6 mol / L, and the complexing agent contains saccharin, oxalic acid, or formic acid, and the molar ratio of the total of the saccharin, oxalic acid, and formic acid to Cr is 1 / 1 to 1 / 26. [A3] In the plating step, the plating temperature is 30 to 65°C, the plating pH is 2.8 to 4.2, and the plating current density is 3 to 10 A / dm ２[A4] The method for producing a trivalent chromium plated product according to [A1] or [A2], wherein the plating electrode uses one or more selected from the group consisting of Ti, Pt, Ir oxide, and Ta. [A4] In the plating step, the plating time is 3 to 30 minutes, the plating electrode distance is 200 to 500 mm, and the plating stirring is 5 to 500 L / min m ２ and preferably 5 to 100 L / min m ２ [A5] The method for producing a trivalent chromium plated product according to any one of [A1] to [A3], wherein the plating electrode uses one or more selected from the group consisting of Ti, Pt, Ir oxide, and Ta. [A6] In the plating step, the plating temperature is 50 to 56°C, the plating pH is 3.0 to 3.8, and the plating current density is 5 to 8 A / dm ２ ) wherein the plating treatment time is 3 to 10 minutes, the plating treatment electrode distance is 250 to 350 mm, and the plating treatment stirring is 5 to 100 L / min·m ２ and preferably 7 to 54 L / min m ２ The method for producing a trivalent chromium plating product according to any one of [A1] to [A4].

[0042] Second Embodiment A method for producing a trivalent chromium-plated product according to this embodiment includes a plating step of applying current to a substrate as a cathode in a trivalent chromium plating solution under the following plating conditions, and a post-treatment step of post-treating the substrate obtained in the plating step by electrolysis or acid immersion. The trivalent chromium-plated product obtained by this method for producing a trivalent chromium-plated product according to this embodiment has excellent corrosion resistance. A method for evaluating the corrosion resistance will be described in the Examples.

[0043] In the plating process of this embodiment, the same configuration as in the first embodiment will be omitted.

[0044] The post-treatment step of this embodiment is a step of post-treating the plated object obtained in the plating step by electrolysis or acid immersion. The electrolysis method is a method of forming a protective coating on the surface layer of the plated object using electrolysis. The acid immersion method is a method of immersing the plated object in an acidic solution to form a protective coating on the surface layer or passivate the plated object. The post-treatment step of this embodiment can further stabilize the surface of the coating.

[0045] The method for producing a trivalent chromium-plated product may further include, in addition to the plating process and the post-treatment process, a pretreatment process for cleaning, a nickel plating process, etc., as necessary. Each process is the same as in the first embodiment.

[0046] Figure 1 is a simplified diagram showing the relationship between the electrode distance and the width of the workpiece in a typical electroplating facility. Anodes are placed facing each other in a plating tank, which is filled with a solution such as a plating solution containing the metal ions to be deposited and a complexing agent.

[0047] The object to be plated is immersed in the solution of a plating tank so that it is positioned between two anodes. Then, a plating process is performed on the object to be plated by passing a current through the object to be plated as the cathode. That is, in the embodiment of the present disclosure, chrome plating is formed from a chemical containing trivalent chromium as a main component. Here, the distance between the anode and the jig that fixes the cathode is defined as the inter-electrode distance.

[0048] When the method for producing a trivalent chromium plated product of this embodiment includes the pretreatment step for the purpose of cleaning, the nickel plating step or other step, the plating treatment step, and the post-treatment step, it is also possible to perform the plating treatment on the plated object by repeating the treatment described above multiple times and adding treatments as needed, such as a water washing treatment, between each treatment.

[0049] [Trivalent chromium plating solution] The trivalent chromium plating solution according to this embodiment contains a Cr source, a complexing agent, an auxiliary complexing agent, a pH buffer, a conductive salt, and a surfactant. The Cr source, the auxiliary complexing agent, the pH buffer, the conductive salt, and the surfactant are the same as those described in the first embodiment.

[0050] <Auxiliary complexing agent> The auxiliary complexing agent is the same as the <Auxiliary complexing agent> described in the first embodiment.

[0051] [Trivalent Chromium Plating Conditions] The method for producing a trivalent chromium-plated product of this embodiment includes a plating process in which an electric current is applied to the substrate as the cathode in the trivalent chromium plating solution under the following plating conditions, and a post-treatment process in which the substrate obtained in the plating process is immersed in acid. Examples of the plating conditions include the plating temperature, plating pH, plating time, plating efficiency, electrode distance, plating stirring speed, and plating electrodes. A good trivalent chromium-plated product can be obtained by combining one or more of these conditions. The plating temperature, plating pH, plating time, plating efficiency, electrode distance, plating stirring speed, and plating electrodes are the same as those described in the first embodiment.

[0052] [Trivalent chromium plating post-treatment conditions] The post-treatment time is preferably 30 to 600 seconds. Furthermore, from the viewpoint of industrially high production efficiency, it is more preferably 60 to 180 seconds. The post-treatment temperature refers to the temperature of the treatment liquid during post-treatment. The post-treatment temperature is preferably 50°C or higher. Furthermore, from the viewpoint of heat drying, it is more preferably about 60°C or higher. The post-treatment temperature may be 90°C or lower. The pH of the post-treatment treatment liquid refers to the pH of the treatment liquid during post-treatment. The pH of the post-treatment treatment liquid is preferably 2.7 to 3.3.

[0053] "Implementation of Manufacturing Method of Second Embodiment" Specific implementations of the manufacturing method of the second embodiment include, for example, the following [B1] to [B5]. [B1] A method for manufacturing a trivalent chromium plated product, comprising: a plating treatment step of passing a current through a trivalent chromium plating solution using an object to be plated as a cathode to obtain a plated product; and a post-treatment step of electrolyzing or acid immersing the plated product obtained in the plating treatment step. [B2] The method for manufacturing a trivalent chromium plated product according to [B1], wherein the post-treatment time is 30 to 600 seconds. [B3] The method for manufacturing a trivalent chromium plated product according to [B1], wherein the post-treatment time is 60 to 180 seconds. [B4] The method for manufacturing a trivalent chromium plated product according to any of [B1] to [B3], wherein in the post-treatment step, the post-treatment uses acid immersion, the post-treatment temperature is 50 to 90°C, and the post-treatment pH is 2.7 to 3.3. [B5] In the plating process, the electrode distance in the plating process is 200 to 500 mm, the temperature in the plating process is 40 to 60°C, and the current density in the plating process is 5 to 10 A / dm ２ The method for producing a trivalent chromium plating product according to any one of [B1] to [B4].

[0054] [Trivalent chromium plating product] The plating film of the trivalent chromium plating product obtained by the manufacturing method of the trivalent chromium plating product of this embodiment not only exhibits the properties of the plating film of the trivalent chromium plating product obtained by the manufacturing method of the first embodiment, but also has excellent corrosion resistance. For example, in the CASS test described below, R.N. is preferably 9.0 or more, more preferably 9.3 or more, and even more preferably 9.5 or more.

[0055] Third Embodiment A method for producing a trivalent chromium-plated product according to this embodiment includes a plating step of applying a current to a substrate as a cathode in a trivalent chromium plating solution, and an ion removal step of removing ions of metals other than Cr using an ion exchange resin that removes ions of metals other than chromium. The "ions of metals other than Cr" include, for example, ions of metals that become impurities, such as Cu and Zn.

[0056] [Ion Exchange Resin] Examples of the ion exchange resin according to this embodiment include styrene-based iminodiacetic acid functional group-type ion exchange resins and styrene-based aminomethyl phosphate functional group-type ion exchange resins. Examples of the styrene-based iminodiacetic acid functional group-type ion exchange resins include commercially available AMBERSEP IRC748 (manufactured by Organo Corporation) and commercially available SurTec IAT (manufactured by SurTec MMC Japan Co., Ltd.). Examples of the styrene-based aminomethyl phosphate functional group-type ion exchange resins include commercially available AMBERSEP IRC747UPS (manufactured by Organo Corporation). By using such ion exchange resins, it is believed that the initially adsorbed trivalent chromium ions are replaced upon contact with divalent metal ions.

[0057] [Trivalent chromium plating solution] The trivalent chromium plating solution according to this embodiment contains a Cr source, a complexing agent, an auxiliary complexing agent, an auxiliary agent, a pH buffer, a conductive salt, and a surfactant. The Cr source, the auxiliary complexing agent, the pH buffer, the conductive salt, and the surfactant are the same as those described in the first embodiment.

[0058] [Trivalent Chromium Plating Conditions] The method for producing a trivalent chromium-plated product of this embodiment includes a plating step in which an electric current is applied to the substrate as the cathode in the trivalent chromium plating solution under the following plating conditions. Examples of the plating conditions include the plating temperature, plating pH, plating stirring speed, and plating electrodes. A good trivalent chromium-plated product can be obtained by combining one or more of these conditions. The plating temperature, plating pH, plating time, and plating electrodes are the same as those described in the first embodiment.

[0059] "Implementation of Manufacturing Method of Third Embodiment" Specific implementations of the manufacturing method of the third embodiment include, for example, the following [C1] to [C4]. [C1] A method for manufacturing a trivalent chromium plated product, comprising: a plating step of applying a current to a substrate as a cathode in a trivalent chromium plating solution; and an ion removal step of removing ions of metals other than Cr, wherein the ion removal step uses an ion exchange resin that removes ions of metals other than Cr. [C2] In the plating step, the plating temperature is 30 to 65°C, the plating pH is 3.0 to 4.2, and the plating current density is 3 to 10 A / dm ２ [C3] In the plating step, the plating time is 3 to 30 minutes, the electrode distance is 200 to 500 mm, and the agitation rate is 5 to 100 L / min·m. ２ [C4] The method for producing a trivalent chromium plated product according to [C1] or [C2], wherein the plating electrode uses one or more selected from the group consisting of Ti, Pt, Ir oxide, and Ta. [C4] In the plating step, the plating temperature is 50 to 56°C, the plating pH is 3.0 to 3.8, and the plating current density is 5 to 8 A / dm ２ ) wherein the plating treatment time is 3 to 10 minutes, the plating treatment electrode distance is 250 to 350 mm, and the plating treatment stirring is 5 to 100 L / min·m ２ The method for producing a trivalent chromium plated product according to any one of [C1] to [C3], wherein the plating treatment electrode uses one or more selected from the group consisting of Ti, Pt, Ir oxide, and Ta.

[0060] The trivalent chromium plating product of this embodiment can be produced by one or a combination of two or more of the embodiments [A1] to [A5] described in the manufacturing method of the first embodiment, the embodiments [B1] to [B5] described in the manufacturing method of the second embodiment, and the embodiments [C1] to [C4] described in the manufacturing method of the third embodiment. For example, it can be produced by a combination of one of the embodiments [A1] to [A5], one of the embodiments [B1] to [B5], and one of the embodiments [C1] to [C4].

[0061] [Hexavalent chromium plating film and manufacturing method thereof] The "hexavalent chromium plating film" of the present disclosure is a decorative chromium plating film formed by a known hexavalent chromium plating method using a known hexavalent chromium plating solution.

[0062] Examples of the known hexavalent chromium plating method and the known hexavalent chromium plating solution include the method and plating solution described in the following Non-Patent Document 1 (e.g., particularly the description on page 91, "3.3.2 Hexavalent chromium bath composition and working conditions"). [Non-Patent Document 1] Plating Textbook, edited by the Electroplating Research Group, published by Nikkan Kogyo Shimbun (1986)

[0063] Examples of the hexavalent chromium plating method include known electrolytic methods. Specific examples include the plating conditions disclosed in the comparative examples described below. Examples of the hexavalent chromium plating solution include an electrolytic solution called a Sargent bath. Examples of the Sargent bath include a plating solution obtained by adding 0.92 g / L of sulfuric acid, a primary catalyst, to an aqueous solution containing 230 g / L of industrial chromic acid, which is 1 / 250 of the chromic acid concentration. The substrate to be plated with hexavalent chromium plating in the present disclosure may be an object of a similar shape to the substrate to be plated with trivalent chromium plating in the present disclosure, or may simply be a flat object such as a test piece. The substrate to be plated with hexavalent chromium plating may be a substrate made of the same material as the substrate to be plated with trivalent chromium plating in the present disclosure, or may be made of a similar material or a different material. It is preferable that the substrate to be plated with hexavalent chromium plating has the same material for at least the outermost chromium plating layer and the layers below it. The substrate to be plated with hexavalent chromium plating, which is the comparison target of the present disclosure, may have the same shape, substrate material, and layer structure as the substrate to be plated with trivalent chromium plating of the present disclosure. For example, the layer structure may be as follows, depending on the material of the substrate. For example, when a copper alloy is used as the substrate, nickel plating is applied to the substrate, and hexavalent chromium plating is applied as the outermost layer thereon. When zinc or a zinc alloy is used as the substrate, copper plating is applied to the substrate, nickel plating is applied thereon, and then hexavalent chromium plating is applied as the outermost layer thereon. When a resin substrate is used as the substrate, the substrate is subjected to a conductive treatment such as electroless plating of copper or nickel, and then semi-bright nickel and bright nickel plating are applied thereon, and hexavalent chromium plating is applied as the outermost layer thereon. From the perspective of providing a trivalent chromium plating product having a glossy appearance similar to that of conventional hexavalent chromium plating, the "conventional hexavalent chromium plating film" of the present disclosure may have the same thickness as a commonly used hexavalent chromium plating film in practice. That is, the film thickness may be different from that of the trivalent chromium plating film of the present disclosure. Specifically, the "conventional hexavalent chromium plating film" of the present disclosure may have a film thickness of 0.1 to 0.5 μm, or may be 0.3 μm.

[0064] The plating film of the trivalent chromium plating product of this embodiment is characterized by a color difference ΔE from the hexavalent chromium plating film of less than 3.5, but may be less than 3±0.5 or even less than 3±0.2, taking into account human eye visibility of color and measurement error. Similarly, the color difference ΔE from the hexavalent chromium plating film is preferably less than 2.0, but may be less than 2±0.5 or even less than 2±0.2. The reference hexavalent chromium plating film was prepared by plating the same type of substrate as the trivalent chromium plating of this embodiment with a Sargent bath containing 230 g / L of chromic acid and 0.92 g / L of sulfuric acid as the electrolyte, at a plating solution temperature of 40°C and a current density of 10 A / dm ２ Preferably, the plating was produced by electroplating under the following conditions: plating time 4 minutes, plating thickness 0.3 μm, same electrode distance (preferably 250 mm), and no stirring. The term "same type of plated object" refers to a plated object having the same material, layer structure, finished surface, shape, and surface area, such as the same spout used in Example A1 and Comparative Example A1, and the same stop valve used in Example A4 and Comparative Example A2. Furthermore, Example D1 and Comparative Example D1, described below, used the same flat plate of nickel-plated brass as the same type of plated object.

[0065] (Trivalent chromium plating film) The trivalent chromium plating film of one embodiment of the present disclosure has a nanostructure with an average crystal grain size (D) of 30 nm or more and 180 nm or less. The trivalent chromium plating film of this embodiment may be subjected to a surface post-treatment with an acid, if necessary. The trivalent chromium plating film preferably has an R.N. of 9.0 or more according to the CASS test method.

[0066] [Average Crystal Grain Size (D)] The method for evaluating the average crystal grain size (D) includes the following steps: Step 1: Using a scanning electron microscope (SEM), one or more, preferably 1 to 10, random test lines are set on the surface of the plating film; Step 2: Calculating the average value by averaging the sum of the lengths of the individual grains (nanostructures) that intersect with the test line by the quotient of the number of measurements, and setting this value as the average crystal grain size.

[0067] [Nanostructure and Crystal Grain Size] The trivalent chromium plating film of this embodiment may be any of the crystalline, microcrystalline, and amorphous plating films shown in Non-Patent Document A below, with microcrystalline plating films being preferred from the viewpoint of corrosion resistance. In this specification, the term "nanostructure" is a broad concept referring to a fine structure of 1 nm to 500 nm, whether crystalline, microcrystalline, or amorphous. Furthermore, the term "crystal grain size" refers to the average grain size of nanoscale (1 nm to 500 nm) particulate structures on the surface of the plating film observed with a scanning electron microscope (SEM), and includes single crystals, microcrystalline aggregates, and amorphous particles. The crystal grain size is evaluated using the average crystal grain size (D). The "crystal grain boundary" in step 2 of the method for evaluating the average crystal grain size (D) refers to the boundary line between the nanostructures. Methods for identifying the boundary line between the nanostructures include visual inspection of SEM images and automatic identification of SEM images using image processing.

[0068] The nanostructure of the trivalent chromium plating film of this embodiment has an average crystal grain size (D) of 30 nm or more and 180 nm or less, preferably 120 nm or less, more preferably 80 nm or less, even more preferably 60 nm or less, and may be 5 nm or more. Furthermore, smaller crystal grain sizes are preferable, making it more difficult for water to penetrate the underlying layer. The range of average crystal grain size (D) includes any combination of upper and lower limits. The trivalent chromium plating film of this embodiment has a nanostructure with an average crystal grain size (D) within the above range, thereby improving corrosion resistance. For example, it is thought that this can prevent substances such as moisture on the plating film surface from penetrating into the plating film and corroding the underlying material. As shown in the principle diagram of Figure 16, it is presumed that the trivalent chromium plating film 62 has fewer voids penetrating into the substrate, thereby suppressing the permeation of moisture and chloride ions 66 and effectively preventing corrosion of the underlying film 64 (e.g., the nickel plating film of Example D1). Furthermore, when the trivalent chromium plating film 62 of this embodiment is formed on the nickel plating film 64, if there are voids or the like penetrating the base, the trivalent chromium plating film is less susceptible to corrosion because the generation potential of oxygen produced by water electrolysis is +0.80 V (SCE), as shown in the principle diagram of Figure 16. However, the Ni plating of the base is corroded by the water that penetrates. It is presumed that the trivalent chromium plating film of the present application, by reducing the number of voids penetrating the base, suppresses the permeation of moisture and chloride ions and effectively prevents corrosion of the nickel plating film of the base film.

[0069] [Non-Patent Document A] Toru Watanabe, Crystallographic Structure of Plated Films, Surface Technology, 1989, Vol. 40, No. 11, pp. 1221-1228.

[0070] [Acid Post-Treatment] The trivalent chromium plating film of this embodiment may further be subjected to an acid post-treatment on its surface, if necessary. The trivalent chromium plating film obtained by acid post-treatment has high corrosion resistance. Furthermore, for example, when the trivalent chromium plating film is a nickel plating film, the corrosion resistance can be improved by passivating the Ni plating in the gaps with acid post-treatment. The acid may be an organic acid or an inorganic acid. Examples of organic acids include nitric acid compounds. Preferred treatment conditions for the post-treatment are, for example, as follows. In the case of acid immersion, an aqueous solution of a nitric acid compound can be used, and commercially available SurTec 880B (manufactured by SurTec MMC Japan Co., Ltd.) was used. Note that equivalent performance can be obtained even with a 1 to 10 g / L aqueous chromic acid solution. In the case of electrolytic chromating, a method was used in which the film was immersed in an aqueous chromium phosphate solution or an aqueous phosphoric acid solution and electrolysis was applied to form a chromate film. The pH of the post-treatment solution was 2.7 to 3.3. The post-treatment conditions were a post-treatment temperature of 50 to 56° C. and a post-treatment time of 70 to 140 seconds.

[0071] [CASS Test Method] The CASS test method is described in Japanese Industrial Standards (JIS) Z 2371 and is a method for evaluating the corrosion state after a test time of 24 hours. The pass / fail criterion is determined by RN 9 or higher (corrosion area ratio of more than 0.07% and 0.10% or less). For example, RN 10 means a corrosion area ratio of 0.00%, and RN 9 means a corrosion area ratio of 0.10% or less.

[0072] The test conditions and method described in JIS Z 2371 are as follows: Reagent: Aqueous solution of 0.26 g / L copper (II) chloride dihydrate and 50 g / L sodium chloride adjusted to pH 3.0-3.1 with acetic acid Spray chamber temperature: 50°C Exposure time: 24 hours

[0073] [Other Properties of Trivalent Chromium Plating Film] The trivalent chromium plating film of this embodiment preferably has a color difference ΔE with a hexavalent chromium plating film of less than 3.5, and more preferably has a color difference ΔE with a hexavalent chromium plating film of less than 2.0. In this case, the trivalent chromium plating film of this embodiment has high corrosion resistance and excellent appearance, and the color difference ΔE with a hexavalent chromium plating film, which is a thin metal film electrolytically produced from an aqueous solution of chromic acid and sulfuric acid, is not noticeable even when mixed with a hexavalent chromium product. The "trivalent chromium plating film" is a chromium metal film formed by electrolytic reduction of trivalent chromium ions. That is, it is a chromium metal film derived from trivalent chromium ions. The "hexavalent chromium plating film" is a chromium metal film formed by electrolytic reduction of hexavalent chromium ions. That is, it is a chromium metal film derived from hexavalent chromium ions. Theoretically, trivalent chromium plating films and hexavalent chromium plating films are the same chromium metal films, but due to differences in the valence of the derived chromium ions, it is assumed that the metal microstructure of each chromium metal film, the trace amounts of components other than chromium, and the mechanical properties of the metal film differ. Furthermore, there is a tendency for the type of derived chromium ion to be indicated on the final product. Therefore, it is recognized that "trivalent chromium plating films" and "hexavalent chromium plating films" are films with different properties.

[0074] The trivalent chromium plating film preferably has a lightness difference ΔL value of less than 2.0 compared to a hexavalent chromium plating film, and more preferably a ΔL value of 1.5 or less. The lightness difference ΔL value may be 0.1 or more, 0.2 or more, 0.5 or more, or even 1.0 or more. The lightness difference ΔL value is the absolute value of the difference between the lightness L of a trivalent chromium plating film obtained using a substrate (substrate) having the same uneven shape and the lightness L of a hexavalent chromium plating film. The trivalent chromium plating film more preferably has a color characteristic a value of +2.0 to -2.0 and a b value of +2.0 to -2.0. From the viewpoint of ensuring high corrosion resistance and excellent appearance, the plating thickness is preferably 0.05 μm or more, and more preferably 0.12 μm or more. Furthermore, from the viewpoint of cost-effectiveness of decorative chromium plating films, the plating thickness of the plating film may be 1 μm or less. More preferably, it is 0.1 to 0.2 μm, and even more preferably, it is 0.2 to 0.4 μm.

[0075] The evaluation of the color of the trivalent chromium plating film, the manufacturing method of the trivalent chromium plating film, and the hexavalent chromium plating film and its manufacturing method are the same as those described in the section on the trivalent chromium plating product and its manufacturing method, and detailed description thereof will be omitted.

[0076] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0077] (Examples A1 to A9, Comparative Examples A1 to A3) Trivalent chromium plating products were produced using a water outlet or a stop valve as the object to be plated, using a trivalent chromium plating solution or a hexavalent chromium plating solution having the composition shown below under the plating conditions shown in Table 1. The trivalent chromium plating film of the trivalent chromium plating product was evaluated, and the results are shown in Table 1. Water outlet: Made of brass, with a relatively smooth surface that was buffed, and in the shape of a pipe with a length of approximately 500 mm and a surface area of ​​3.62 dm ２ (471 g) and two pieces were used. Stopcock: Made of brass, finished with #800 finish, with a relatively uneven surface, a small block shape with angular recesses, and a surface area of ​​0.76 dm ２(149 g) and six pieces were obtained.

[0078] [Plating Solution Composition in Each Example and Comparative Example] <Composition of Trivalent Chromium Plating Solution> A plating solution containing approximately 0.5 mol / L of chromium (III) sulfate or basic chromium (III) sulfate as a Cr supply source, saccharin as a complexing agent at a molar ratio to Cr of approximately 1 / 15, 70 to 100 g of boric acid as an auxiliary agent, 150 to 230 g of sodium sulfate as a conductive salt, and a small amount of alkylsulfosuccinic acid is used. A commercially available plating solution with similar components, Sutec 883XT (manufactured by Surtec MMC Japan Co., Ltd.), may also be used.

[0079] <Composition of hexavalent chromium plating solution> An electrolytic solution generally called a Sargent bath was used as the hexavalent chromium plating solution. Specifically, 0.92 g / L of sulfuric acid, which is 1 / 250 of the amount of chromic acid, was added as a primary catalyst to an aqueous solution containing 230 g / L of industrial chromic acid.

[0080] The electrode distance, stirring, CASS test, and evaluation methods for appearance and color tone shown in Table 1 will be explained below.

[0081] 2 and 3 are simplified diagrams showing the principle of the relationship between the electrode distance and the width of the workpiece in a typical electroplating facility. Anodes are placed facing each other in a plating tank, which is filled with a solution such as a plating solution containing the metal ions to be deposited and a complexing agent.

[0082] The object to be plated is immersed in the solution of a plating tank so that it is positioned between two anodes. Then, a plating process is performed on the object to be plated by passing a current through the object to be plated as the cathode. That is, in the embodiment of the present disclosure, chrome plating is formed from a chemical containing trivalent chromium as a main component. Here, the distance between the anode and the jig that fixes the cathode is defined as the inter-electrode distance.

[0083] As shown in the principle diagrams of Figures 2 and 3, the effect on the plating film varies depending on the ratio of the width of the workpieces 21 and 31 to the inter-electrode distance (horizontal in Figure 1). Even if Figures 2 and 3 have the same inter-electrode distance (d21, d22, d31, d32), the width (direction between the electrodes, horizontal in Figure 1) in Figure 3 is larger, so the inter-electrode distance in Figure 3 has a greater effect on plating than in Figure 2. For example, in the case of the spout shown in Figure 2, the outer diameter is 30 mm, the inter-electrode distance (d21, d22) is 250 mm, the position D22 closest to the electrode is 250 mm - 30 mm / 2 = 235 mm, and the position D21 farthest from the electrode is 250 mm. The ratio of these distances is 0.94. The inter-electrode distance (d21, d22) is 250 mm. On the other hand, in the case of the bath faucet shown in Figure 3, the height is 70 mm, the electrode distance (d31, d32) is 250 mm, the position D32 closest to the electrode is 250 - 70 m = 180 mm, the position D31 farthest is 250 mm, and the ratio of these distances is 0.72. If this electrode distance (d21, d22, d31, d32) is 200 mm, a water outlet with no depth has a distance ratio of 0.93 and is less affected, but in the case of a bath faucet, the distance ratio is 0.65, and the deeper the object to be plated, the more pronounced the difference depending on the location.

[0084] <Agitation strength> When using air agitation instead of mechanical agitation, the agitation force weakens as the liquid surface area increases, even if the amount of air blown in is the same. ２ The flow strength was expressed as the amount of air blown in per minute relative to the liquid surface area of ​​2750 cm. ２ The flow strength was expressed as the amount of air blown in per minute relative to the liquid surface area of ​​2750 cm. ２ The air blown in per minute is 15L or more (ejection volume: 54L / min m ２ ). During stirring, the liquid surface area is 2750 cm ２ The amount of air blown in per minute is 10 to 15 L, and the amount of air blown in per minute is 36 to 54 L / min. ２ ). Weak stirring means a liquid surface area of ​​2750 cm ２ The amount of air blown in per minute is 2 to less than 6 L (amount of air blown in per minute: 7 to 21 L / min.m ２ ).

[0085] <CASS Test> The CASS test method is described in Japanese Industrial Standards JIS Z 2371, and is a method for evaluating the corrosion state after a test time of 24 hours. The pass / fail criterion is R.N. 9 or higher (corroded area ratio of more than 0.07% and 0.10% or less).

[0086] <Color Tone> The colors of the coating surface of the trivalent chromium plating product and the coating surface of the hexavalent chromium plating product were measured using a color difference meter (a CR-400 color difference meter manufactured by Konica Minolta, Inc., measurement conditions: SCI). The L*a*b* values ​​in the L*a*b* color system were measured. In addition, the color difference ΔE in the color change of the coating surface of the trivalent chromium plating product was calculated based on the color of the coating surface of the hexavalent chromium plating product of the same type of plated object (substrate). For example, the plated products of Examples A1 to A3 and A7 to A9 were compared with the plated product of Comparative Example A1, and the plated products of Examples A4 to A6 were compared with the plated product of Comparative Example A2. Note that the hexavalent chromium plating product used as the reference was the same type of plated object as the trivalent chromium plating product being calculated.

[0087] <Appearance> Appearance evaluation of the plated object is performed visually. If the plated object has cloudy or water droplet patterns in some areas, it is rated as "B." If the appearance is indistinguishable from that of a hexavalent chromium plated product, it is rated as "A."

[0088] <Throwing power> The method for evaluating throwing power is shown in Figures 4 and 5. Ideally, full coverage is achieved, but because it depends on the shape, it is evaluated on a product-by-product basis. For example, in the example of object 41 shown in Figure 4, Cr is deposited at corners (right-angled recesses) 49, which represents ideal plating throwing power. In other words, the throwing power is good. On the other hand, in the example of object 51 shown in Figure 5, Cr is not deposited at corners (right-angled recesses) 59, resulting in insufficient throwing power. Throwing power is determined from the length of Cr plating deposited from the edge toward the obtuse angle (e.g., t in Figure 5).

[0089]

[0090] The meaning of each symbol in Table 1 is explained below: Object to be plated S: Spout, V: Stopcock Plating solution T: Trivalent chromium, H: Hexavalent chromium *1: Theoretical calculation *2: Not measured or evaluated because Cr was not deposited.

[0091] (Examples B1 to B8) Trivalent chromium plating products were formed in the same manner as in Example A1, except that the plating conditions in Table 2 were used. Then, the plated object obtained in the plating process was post-treated by acid immersion. The color difference ΔE of the trivalent chromium plating film of the trivalent chromium plating product was calculated in the same manner as in Example A1. The color difference ΔE of Examples B1 to B8 was all less than 2.0. Furthermore, a CASS test was conducted using the above method. The evaluation results are shown in Table 2.

[0092]

[0093] In Table 1, the meaning of each symbol is explained below: Object to be plated V: Stopcock plating solution T: Trivalent chromium

[0094] <Post-treatment step> The composition of the post-treatment solution is as follows. In the case of acid immersion, an aqueous solution of a nitric acid compound can be used, and commercially available SurTec 880B (manufactured by SurTec MMC Japan Co., Ltd.) was used. Note that equivalent performance can be obtained using a 1 to 10 g / L aqueous chromic acid solution. In the case of electrolytic chromating, a method was used in which the sample was immersed in an aqueous chromium phosphate solution or an aqueous phosphoric acid solution and electrolysis was applied to form a chromate coating. The pH of the post-treatment solution was 2.7 to 3.3. The post-treatment conditions were a post-treatment temperature of 50 to 56°C and a post-treatment time of 70 to 140 seconds.

[0095] (Example C1) An ion exchange resin (AMBERSEP IRC748, size, ion exchange resin amount: volume 1.2 L (volume 1 / 100 of the plating solution) was used to remove ions of metals other than Cr. The ion removal step was performed in the same manner as in Example A1, and a trivalent chromium plated product was formed. For the water outlet as the plated object, 8 portions of trivalent chromium were plated and repeatedly immersed in the solution for 40 minutes. As a result, approximately 450 water outlets (plated area 1707 dm ２When plating was performed on a copper alloy substrate, no cloudiness occurred in the resulting trivalent chromium plating film. Copper and zinc ions eluted from copper alloy substrates into the plating solution are difficult to precipitate in hexavalent chromium plating solution, but they precipitate easily in trivalent chromium plating solution, so the tolerance level is small. In the case of resin, although Ni plating solution may be carried over from the previous process, there is no elution from the substrate. When plating on metal, elution from exposed parts such as the inside of the substrate is significant, so it is important to constantly adsorb and remove them.

[0096] The ion exchange resin conditions were as follows: Amount of ion exchange resin: 1.2 L in volume (volume 1 / 100 of the plating solution); Circulation flow rate to ion exchange resin: 2 L / min for 120 L (surface velocity approximately 90 mm / min = speed passing through the resin).

[0097] (Comparative Example C1) A trivalent chromium-plated product was formed in the same manner as in Example A1, using an ion exchange resin, SurTec 880IAT (manufactured by SurTec MMC Japan Co., Ltd.), which adsorbs and removes ions of metals other than Cr, with a resin volume of 1.2 L (volume 1 / 100 of the plating solution). Eight portions of a water outlet were plated with trivalent Cr, and the water outlet was repeatedly immersed in the solution for 40 minutes. As a result, approximately 450 water outlets (total plated area 1707 dm ２ When the plating was performed, no clouding occurred on the film of the trivalent chromium plating product. The ion exchange resin conditions were as follows: Amount of ion exchange resin: 1.2 L in volume (resin volume is 1 / 100 of the plating solution) Circulation flow rate to the ion exchange resin: 2 L / min for 120 L (surface speed is approximately 90 mm / min = speed passing through the resin)

[0098] FIG. 6 shows the relationship between the concentration of various ions other than Cr and the amount of immersion when trivalent Cr plating is performed for 8 minutes and then the plating is repeatedly immersed in the solution for 40 minutes, in a case where the ion removal process using an ion exchange resin to remove ions of metals other than Cr is not included.

[0099] (Reference Example C1) Figure 7 shows the relationship between the untreated solution volume and elapsed time when 120 L of plating solution was passed through the ion exchange resin at a circulation rate of 2 L / min, when an ion removal step using an ion exchange resin to remove ions of metals other than Cr was included. Measurement of various ions at the time of cloudiness revealed Ni: 14.6 ppm, Cu: 3.7 ppm, and Zn: 1.3 ppm. Figure 8 shows the relationship between the concentration of various ions other than Cr and elapsed time when 120 L of plating solution was passed through the ion exchange resin at a circulation rate of 2 L / min, when an ion removal step using an ion exchange resin to remove ions of metals other than Cr was included. As shown in Figures 7 and 8, under these conditions, theoretically, 98% of the plating solution can be circulated in approximately 240 minutes. Furthermore, the concentrations of Ni and Zn ions reached approximately 0 ppm after approximately 240 minutes, suggesting that the exchange efficiency is close to 100%.

[0100] (Method of Evaluating Fogging) Judging by visual inspection. If the fogging is not noticeable, it is judged that there is no fogging, and if the fogging is noticeable, it is judged that there is no fogging.

[0101] (Examples D1 to D6, Comparative Example D1) Using the same Ni-plated brass flat plate as the substrate, a trivalent chromium plating film was produced on the substrate using a trivalent chromium plating solution or hexavalent chromium plating solution having the composition shown below under the plating conditions shown in Table 3. The evaluation results of the trivalent chromium plating film are shown in Table 1.

[0102] [Plating Solution Composition in Each Example and Comparative Example] <Composition of Trivalent Chromium Plating Solution> A plating solution containing approximately 0.5 mol / L of chromium (III) sulfate or basic chromium (III) sulfate as a Cr supply source, saccharin as a complexing agent at a molar ratio to Cr of approximately 1 / 15, 70 to 100 g of boric acid as an auxiliary agent, 150 to 230 g of sodium sulfate as a conductive salt, and a small amount of alkylsulfosuccinic acid is used. A commercially available plating solution with similar components, Sutec 883XT (manufactured by Surtec MMC Japan Co., Ltd.), may also be used.

[0103] <Composition of hexavalent chromium plating solution> An electrolytic solution generally called a Sargent bath was used as the hexavalent chromium plating solution. Specifically, 0.92 g / L of sulfuric acid, which is 1 / 250 of the amount of chromic acid, was added as a primary catalyst to an aqueous solution containing 230 g / L of industrial chromic acid.

[0104] The stirring amount, average crystal grain size (D), CASS test, and evaluation methods for appearance and color tone shown in Table 1 will be explained below.

[0105] <Amount of agitation> When using air agitation instead of mechanical agitation, the agitation force weakens as the liquid surface area increases, even if the amount of air blown in is the same. Therefore, the agitation strength is adjusted based on the liquid surface area of ​​2750 cm ２ The flow strength was expressed as the amount of air blown in per minute relative to the liquid surface area of ​​2750 cm. ２ The flow strength was expressed as the amount of air blown in per minute relative to the liquid surface area of ​​2750 cm. ２ The air blown in per minute is 15L or more (ejection volume: 54L / min m ２ ). During stirring, the liquid surface area is 2750 cm ２ The amount of air blown in per minute is 10 to 15 L, and the amount of air blown in per minute is 36 to 54 L / min. ２ ). Weak stirring means a liquid surface area of ​​2750 cm ２ The amount of air blown in per minute is 2 to less than 6 L (amount of air blown in per minute: 7 to 21 L / min.m ２ ).

[0106] <Scanning Electron Microscope (SEM)> Using a Zeiss scanning electron microscope (SEM) (accelerating voltage: 0.8 kV), surface images of the samples of each example and comparative example were measured at a magnification of 50,000. The results are shown in Figures 2 to 7.

[0107] <Average Crystal Grain Size (D)> The average crystal grain size (D) was measured using the above-described method with a microscope scale (M) of 50,000 and one test line.

[0108] <CASS Test> The CASS test method was the same as that described above.

[0109] <Color Tone> The colors of the surfaces of the trivalent chromium plating films and the hexavalent chromium plating films were measured using a color difference meter (a CR-400 color difference meter manufactured by Konica Minolta, Inc., measurement conditions: SCI). The L*a*b* values ​​in the L*a*b* color system were measured. In addition, the color difference ΔE in the color change of the surface of the trivalent chromium plating film was calculated based on the color of the surface of the hexavalent chromium plating film of the same type of plated object (substrate). For example, the trivalent chromium plating films of Examples D1 to D6 were compared with the hexavalent chromium plating film of Comparative Example D1. Note that the hexavalent chromium plating film used as the reference was made on the same type of plated object as the trivalent chromium plating film to be calculated.

[0110]

[0111] In Table 1, the meaning of each symbol is explained below. Plating solution T: trivalent chromium, H: hexavalent chromium *1: Theoretical calculation

[0112] 1, 21, 31, 41: Object to be plated 2A, 2B, 22A, 22B, 32A, 32B: Anode 3, 23, 33: Cathode (jig) 4, 24, 34: Plating solution 5, 25, 35: Plating tank 46, 56: Coating 47, 57: Base layer (nickel plating film) 48, 58: Base material 49, 59: Corner (right-angled recess) 10, 20, 30: Plating equipment 62: Trivalent chromium plating film 64: Base film, nickel plating film 66: Moisture and chloride ions D21, D31: Farthest position D22, D32: Closest position to electrode d21, d22, d31, d32: Distance between electrodes t: Length

Claims

A trivalent chromium plating product, The plating film of the trivalent chromium plating product is characterized in that the color difference ΔE from the hexavalent chromium plating film is less than 3.

5. The trivalent chromium plating product according to claim 1, wherein the plating film of the trivalent chromium plating product has a color difference ΔE from a hexavalent chromium plating film of less than 2.

0. The plating film of the trivalent chromium plating product has a lightness difference ΔL value with respect to the hexavalent chromium plating film of less than 2.0, The trivalent chromium plating product according to claim 1, wherein the color characteristics are a value of +2.0 to -2.0 and b value of +2.0 to -2.

0. The trivalent chromium plating product according to claim 1, wherein the thickness of the plating film of the trivalent chromium plating product is 1 μm or less. 　 The trivalent chromium plating product according to claim 1, wherein the thickness of the plating film of the trivalent chromium plating product is 0.05 μm or more and 0.4 μm or less. 　 The trivalent chromium plating product according to claim 1, wherein the plating film of the trivalent chromium plating product has an L value of 65 to 90 (ΔL less than 2.0), an a value of +0.5 to −1.0, and a b value of +1.0 to −1.

5. A trivalent chromium plating product obtained by the method for producing a trivalent chromium plating product, The method for producing the trivalent chromium plating product includes a plating treatment step of applying electricity to an object to be plated as a cathode in a trivalent chromium plating solution, The trivalent chromium plating solution contains a Cr source and a complexing agent, the Cr supply source is at least one selected from the group consisting of chromium compounds of sulfuric acid, basic sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid; The trivalent chromium plating product according to claim 1, wherein the complexing agent is at least one selected from the group consisting of saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, and carboxylic acid derivatives. 　 A trivalent chromium plating product obtained by the method for producing a trivalent chromium plating product, The method for producing the trivalent chromium plating product comprises: a plating process in which an electric current is passed through a trivalent chromium plating solution to form a plated object using the object as a cathode; The trivalent chromium plated product according to claim 1, further comprising a post-treatment step of electrolyzing or acid-immersing the plated product obtained in the plating treatment step. 　 A trivalent chromium plating product obtained by the method for producing a trivalent chromium plating product, The method for producing the trivalent chromium plating product comprises: a plating treatment step of passing electricity through a substrate as a cathode in a trivalent chromium plating solution; an ion removal step of removing ions of metals other than Cr, The trivalent chromium plating product according to claim 1, wherein the ion removal step uses an ion exchange resin that removes ions of metals other than Cr. A trivalent chromium plating film having a nanostructure with an average crystal grain size (D) of 30 nm or more and 180 nm or less. The average crystal grain size (D) was evaluated as follows: setting one or more random test lines on the surface of the trivalent chromium plating film using a scanning electron microscope (SEM); The method includes a step of calculating an average value by dividing the sum of the lengths of the individual grains (nanostructures) that intersect with the test line by the number of measurements, and determining the average crystal grain size. The trivalent chromium plating film according to claim 10, having a nanostructure with an average crystal grain size (D) of 50 nm or more and 120 nm or less. 　 The trivalent chromium plating film according to claim 10 or 11, wherein the surface of the trivalent chromium plating film is post-treated with an acid. The trivalent chromium plating film according to claim 10 or 11, having a plating thickness of 0.05 μm or more. 　 The trivalent chromium plating film according to claim 10 or 11, having an R.N. of 9.0 or more according to the CASS test method. The CASS test method is described in Japanese Industrial Standards JIS Z 2371, and is a method for evaluating the state of corrosion after a test time of 24 hours. R.N. 10 means a corrosion area ratio of 0.00%, R.N. 9 means a corrosion area ratio of 0.10%, and R.N. 9.0 or higher means a corrosion area ratio of 0.10% or less. 　 A trivalent chromium plating product having the trivalent chromium plating film according to claim 10 or 11. 　 A method for producing a trivalent chromium plated product, comprising a plating process step of applying current to a substrate as a cathode in a trivalent chromium plating solution, The trivalent chromium plating solution contains a Cr source and a complexing agent, the Cr source includes at least one selected from the group consisting of chromium compounds of sulfuric acid, basic sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid; the complexing agent contains at least one organic acid selected from the group consisting of saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, and carboxylic acid derivatives; The method for producing a trivalent chromium plating product, wherein the plating film of the trivalent chromium plating product has a color difference ΔE from a hexavalent chromium plating film of less than 3.

5. In the plating film of the trivalent chromium plating product, The difference in lightness ΔL from the hexavalent chromium plating film is less than 2.0, The method for producing a trivalent chromium plated product according to claim 16, wherein the color characteristics are such that the a value is +2.0 to −2.0 and the b value is +2.0 to −2.

0. The method for producing a trivalent chromium plating product according to claim 16 or 17, wherein the plating coating of the trivalent chromium plating product has a thickness of 0.05 μm or more and 1 μm or less. 　 The Cr source is not a chromium compound such as hydrochloric acid, nitric acid, or phosphoric acid, the Cr source comprises chromium (III) sulfate or basic chromium (III) sulfate, and the concentration of the chromium (III) sulfate or basic chromium (III) sulfate is 0.4 to 0.6 mol / L; The complexing agent contains saccharin, oxalic acid, or formic acid, and the molar ratio of the total of saccharin, oxalic acid, and formic acid to Cr is 1 / 2 to 1 / 20. The method for producing a trivalent chromium plating product according to claim 16 or 17. 　 In the plating treatment step, The plating temperature is 30 to 65°C, The plating treatment pH is 2.8 to 4.2, Plating current density is 3 to 10 A / dm ２ ) and The method for producing a trivalent chromium plated product according to claim 16 or 17, wherein the plating treatment electrode uses one or more selected from the group consisting of Ti, Pt, Ir oxide, and Ta. 　 In the plating treatment step, The plating time is 3 to 30 minutes, The plating efficiency is 0.1 to 10%; The plating process electrode distance is 200 to 500 mm, Plating treatment stirring speed: 5 to 500 L / min. ２ and The method for producing a trivalent chromium plated product according to claim 16 or 17, wherein the plating treatment electrode uses one or more selected from the group consisting of Ti, Pt, Ir oxide, and Ta. 　 In the plating treatment step, The plating temperature is 50 to 56°C, the plating treatment pH is 3.0 to 3.8, The plating treatment current density is 5 to 8 A / dm ２ ) and The plating time is 3 to 10 minutes, The plating process electrode distance is 250 to 350 mm, Plating treatment stirring speed: 7 to 54 L / min. ２ The method for producing a trivalent chromium plating product according to claim 20.

Images