Method for producing trivalent chromium plated product and trivalent chromium plated product

Abstract

To provide a method for producing a trivalent chromium plated product having corrosion resistance, and to provide a trivalent chromium plated product.SOLUTION: The method for producing a trivalent chromium plated product of the present invention is a method for producing a plated product having a trivalent chromium plating film. The method for producing a trivalent chromium plated product of the present invention includes a plating treatment step of applying a current to an object to be plated as a cathode in a trivalent chromium plating solution to obtain a plated product, and a post-treatment step of electrolyzing or acid-immersing the plated product obtained in the plating treatment step.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a trivalent chromium plated product and a trivalent chromium plated product. [Background technology]

[0002] Hexavalent chromium plating solutions are widely used in the metal finishing industry for both decorative and hard chrome plating because chrome plating gives a silvery luster and has excellent corrosion resistance. However, in recent years, with consideration given to the environment, development has progressed in plating solutions that contain trivalent chromium and do not use hexavalent chromium. On the other hand, it has generally been difficult to obtain the same performance as hexavalent chromium plating with plating solutions containing trivalent chromium. For example, to obtain a trivalent chromium coating, a complexing agent must be added to the plating solution to precipitate the chromium. However, this causes organic matter to be incorporated into the chromium coating, resulting in significant discoloration due to a decrease in purity, so the deposition rate must be slowed down compared to hexavalent chromium.

[0003] In recent years, various trivalent chromium plating solutions that aim to achieve the same performance as hexavalent chromium plating have been reported, such as a method for improving the corrosion resistance of a trivalent chromium coating (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2021-507114 Summary of the Invention [Problem to be solved by the invention]

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

[0006] The present disclosure has been made in view of the above circumstances, and provides a method for producing a corrosion-resistant trivalent chromium-plated product, and the trivalent chromium-plated product. [Means for solving the problem]

[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] That is, the present invention includes the following aspects. [1] A method for producing a plating product having a trivalent chromium plating film, 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; A method for producing a trivalent chromium plated product, comprising: a post-treatment step of electrolyzing or acid-immersing the plated product obtained in the plating treatment step. [2] The method for producing a trivalent chromium plating product according to [1], wherein the thickness of the plating film of the trivalent chromium plating product is 0.2 μm or more. [3] The method for producing a trivalent chromium plating product according to [2], wherein the thickness of the plating film of the trivalent chromium plating product is 0.2 to 1.0 μm. [4] The method for producing a trivalent chromium plated product according to any one of [1] to [3], wherein the post-treatment time is 30 seconds to 600 seconds. [5] The method for producing a trivalent chromium plating product according to [4], wherein the post-treatment time is 60 to 180 seconds. [6] In the post-treatment step, the post-treatment is performed by acid immersion, Post-treatment temperature is 50 to 90°C The method for producing a trivalent chromium plating product according to any one of [1] to [5], wherein the post-treatment pH is 2.7 to 3.3. [7] In the plating treatment step, The electrode distance for plating is 200 to 500 mm. The plating temperature is 40 to 60°C. The current density of the plating process is 5 to 10 A / dm 2 The method for producing a trivalent chromium plating product according to any one of [1] to [6], [8] A trivalent chromium plating product obtained by the method for producing a trivalent chromium plating product according to any one of [1] to [7], A trivalent chromium plating product characterized in that the plating film of the trivalent chromium plating product has a color difference ΔE of less than 3.5 from a hexavalent chromium plating film. [9] The plating film of the trivalent chromium plating product has a difference in brightness ΔL value with respect to the hexavalent chromium plating film of less than 2.0, The trivalent chromium plating product described in [8] has color characteristics of a value of +2.0 to -2.0 and b value of +2.0 to -2.0.

[10] The trivalent chromium plating product according to [8] or [9], wherein the thickness of the plating film of the trivalent chromium plating product is 0.2 μm or more and 1.0 μm or less.

[11] The trivalent chromium plating product according to any one of [8] to

[10] , wherein the plating film of the trivalent chromium plating product has an L value of 65 to 90, a lightness difference ΔL value from a hexavalent chromium plating film of less than 2.0, an a value of +0.5 to -1.0, and a b value of +1.0 to -1.5. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a principle diagram of a trivalent chromium plating apparatus according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is a principle diagram showing the relationship between the electrode distance and the width of the object to be plated in one embodiment of the present disclosure (when the width of the object to be plated is small). [Figure 3] FIG. 3 is a principle diagram showing the relationship between the electrode distance and the width of the object to be plated in one embodiment of the present disclosure (when the object to be plated has a large width). [Figure 4] FIG. 4 is a principle diagram for explaining a method for evaluating the throwing power of a chrome-plated product (when the throwing power is good). [Figure 5]FIG. 5 is a principle diagram for explaining a method for evaluating the throwing power of a chrome plating product (when the throwing power is insufficient). DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] (Method of manufacturing trivalent chromium plating products) A method for producing a trivalent chromium plated product according to one embodiment of the present disclosure is a method for producing a plated product having a trivalent chromium plating film. The method for producing a trivalent chromium plated product according to this embodiment includes a plating step in which a substrate to be plated is used as a cathode and an electric current is applied in a trivalent chromium plating solution to obtain a plated product, and a post-treatment step in which the plated product obtained in the plating step is electrolyzed or immersed in acid. 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 corrosion resistance will be described in the Examples.

[0012] FIG. 1 shows the principle of the trivalent chromium plating apparatus of 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 main 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 Ir-Ta composite oxide thin film. The cathode 3 is electrically connected to the workpiece 1. If necessary, a stirring device (not shown) for stirring the trivalent chromium plating solution 4 may be provided.

[0013] Figures 2 and 3 are simplified diagrams showing the principle of the relationship between the electrode distance and the width of the workpiece in typical electroplating equipment. Anodes are placed facing each other in the plating tank, which is filled with a solution such as a plating solution containing the metal ions to be deposited and a complexing agent.

[0014] The object to be plated is immersed in the solution of the plating tank so that it is positioned between two anodes. Then, the object to be plated is plated by passing an electric 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.

[0015] 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.

[0016] The method for producing a trivalent chromium-plated product of the present embodiment may include, in addition to the above-mentioned plating treatment step, steps such as a pretreatment step for cleaning and a nickel plating step, as necessary.

[0017] The pretreatment processes for the purpose of cleaning include dissolving metal surfaces and processing oils that have oxidized over time, removing machining oils with alkali, 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 combining these processes appropriately, the substrate can be made more suitable for plating. In the embodiment of the present disclosure, it is not necessary to provide a pre-treatment step. Although examples of the pre-treatment step have been described above, the present disclosure is not limited to the above, and any suitable pre-treatment steps may be selected and combined as needed, and the order of the pre-treatment steps is not limited.

[0018] 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.

[0019] 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.

[0020] [Item to be plated] The substrates used for plating include iron substrates such as non-ferrous copper alloys, zinc, zinc alloys, and stainless steel, as well as resin substrates. For example, when a copper alloy substrate is used, nickel plating is applied to the substrate, followed by a 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 a 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 a chrome plating as the outermost layer. This layer 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 object to be plated in this embodiment may be an object that has already been treated by the above-mentioned nickel plating step, etc. 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 object may be one that has been treated by the above-mentioned nickel plating, the above-mentioned copper plating / nickel plating, or the above-mentioned copper or nickel electroless plating / nickel plating.

[0021] [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. Also, as a commercially available plating solution, there is the chemical SurTec883XT (manufactured by SurTec MMC Japan Co., Ltd.).

[0022] [<Cr source>] Examples of the Cr source include chromium compounds such as sulfuric acid, basic sulfuric acid, hydrochloric acid, nitric acid, and phosphoric acid. The Cr source is preferably a sulfuric acid-based compound in which unnecessary substances unintended in the film are difficult to be incorporated. More preferably, it is chromium(III) sulfate or basic chromium(III) sulfate. The content of the Cr source in the trivalent chromium plating solution is not particularly limited, but for example, in terms of Cr ion conversion, it is preferably 0.3 to 1.0 mol / L, and more preferably 0.4 to 0.6 mol / L.

[0023] [<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 derivatives of the organic acids include amides such as saccharin, and sodium, potassium, and ammonium salts of the carboxylic acids. Specific examples of the organic acids include, for example, acetic acid, oxalic acid, formic acid, succinic acid, lactic acid, maleic acid, malonic acid, malic acid, carboxylic acid, tricarboxylic acid, aminocarboxylic acid, tartaric acid, glycine, etc. The complexing agent is preferably saccharin, oxalic acid with a small molecular weight, or formic acid, which is difficult to be incorporated into the film. More preferably, it is saccharin. For example, when obtaining a trivalent chromium coating, a complexing agent must be added to the plating solution to facilitate chromium deposition. This results in organic matter being incorporated into the chromium coating, which tends to result 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, by including them, chromium deposition occurs against the predominant water electrolysis, resulting in the deposition of chromium ions. Specifically, they can make chromium deposition more dominant than water electrolysis, thereby promoting the deposition of chromium ions. Specifically, trivalent chromium ions have a more positive potential than hexavalent chromium ions, so even if the energy is increased, water electrolysis prevails and chromium deposition does not occur. Therefore, when depositing trivalent chromium ions, complexing can be used to control the potential to favor deposition. The content of the complexing agent in the trivalent chromium plating solution is not particularly limited, but for example, the molar ratio of the complexing agent to Cr is preferably 1 / 1 to 1 / 26, and more preferably 1 / 10 to 1 / 17. 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.

[0024] <Adjuvants> Auxiliaries are added to adjust various properties of the plating solution, including corrosion resistance, complex formation, color adjustment, plating solution life extension, and efficiency adjustment. The adjuvant is preferably, for example, an organic compound, an inorganic acid, or an alcohol. More specifically, examples thereof 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 adjuvants can be appropriately selected and used in combination. The content in the trivalent chromium plating solution may be added according to the plating state and is not particularly limited.

[0025] <pH buffer> Examples of the pH buffer include boric acid or salts of boric acid. Boric acid serves to buffer the pH of the product surface during plating from shifting to alkaline. On the other hand, it has the property of being prone to crystallization at low temperatures depending on the concentration. By adjusting to an appropriate content, a good appearance can be obtained. The content of the pH buffer in the trivalent chromium plating solution is not particularly limited, but for example, it is preferably 40 to 100 g / L, more preferably 70 to 90 g / L.

[0026] <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 affects the inter-electrolyte resistance of the plating solution. By setting an appropriate content, a good appearance can be obtained. If the amount is insufficient, the inter-electrolyte resistance will increase. On the other hand, since there is a limit to the dissolution amount, adjustment to an appropriate content is required. The content of the conductive salt in the trivalent chromium plating solution is not particularly limited, but sulfuric acid-based salts of the same series as the anion used in the Cr supply source are preferred. For example, the content of sodium sulfate is preferably 100 to 250 g / L, more preferably 150 to 230 g / L.

[0027] <Surfactant> Examples of the surfactant include succinic acid, sulfosuccinic acid, alkyl sulfosuccinic acid, dodecylbenzenesulfonic acid, alcohols, etc. The surfactant plays a role in enhancing the affinity between the metal plating surface and the solution. Therefore, the adhesion strength can be maintained. The content of the surfactant in the trivalent chromium plating solution is not particularly limited, but for example, alkyl sulfosuccinic acid is preferably 0.03 to 0.90 g / L, more preferably 0.05 to 0.18 g / L.

[0028] [Trivalent chromium plating treatment conditions] The method for producing a trivalent chromium-plated product of the present embodiment includes a plating step of passing a current through the substrate as a cathode in the above-mentioned trivalent chromium plating solution under the following plating conditions, and a treatment step of post-treating the substrate obtained in the plating step by immersing it in acid. The plating conditions include, for example, plating temperature, plating pH, plating time, plating efficiency, electrode distance, stirring speed, or electrodes, etc. A good trivalent chromium plating product can be obtained by using one or a combination of two or more of these.

[0029] The plating temperature refers to 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.

[0030] 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.

[0031] The plating 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.

[0032] The plating treatment time is the time for which current is passed. The plating treatment time is preferably 3 to 30 minutes, and more preferably 5 to 10 minutes. Within this treatment time range, a better color tone can be obtained. The distance between electrodes during plating is preferably 200 to 500 mm, and more preferably 250 to 350 mm. The plating process stirring speed is the speed at which the solution is stirred. The plating process stirring speed is 5 to 100 L / min m 2 is preferable, and more preferably 7 to 54 L / min m2 is. The plating electrode preferably uses one or more materials selected from the group consisting of Ti, Pt, Ir oxide, and Ta.

[0033] [Trivalent chromium plating post-treatment conditions] The post-treatment time is preferably 30 to 600 seconds, and more preferably 60 to 180 seconds from the viewpoint of industrially high production efficiency. The post-treatment temperature is the temperature of the treatment solution during post-treatment. The post-treatment temperature is preferably 50°C or higher. From the viewpoint of heat drying, the post-treatment temperature is more preferably about 60°C or higher. The post-treatment temperature may be 90°C or lower. The pH of the post-processing solution is the pH of the processing solution during post-processing, and the pH of the post-processing solution is preferably 2.7 to 3.3.

[0034] [Evaluation of trivalent chromium plating film] <Color difference ΔE> When the colors of the standard 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.

[0035] ΔE=√((L6-L3) 2 +(a6-a3) 2 +(b6-b3) 2 )

[0036] For example, if the differences are L = 2, a = 2, and b = 2, ΔE=√(4+4+4)=√12=3.46. The plating solution and plating conditions used for the reference hexavalent chromium plating will be explained later. The substrate (object 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 be free from the influence of the reflectance that changes due to the unevenness of the substrate.

[0037] <Lightness difference ΔL value> The appearance of trivalent chromium plated products can be expressed using the a-value, b-value, and L-value. The L-value here refers to brightness, which 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 brightness difference ΔL, which eliminates the effect of reflectance that varies with substrate irregularities. Specifically, using substrates with the same irregularities, hexavalent chromium plating and trivalent chromium plating are performed, respectively. The absolute value ΔL of the difference between the brightness L6 of the resulting hexavalent chromium plating film and the brightness 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 coating has L6=72.85, while the trivalent chromium plating coating of this embodiment has L3=72.50. 6 =86.68, and trivalent chromium plating film has L3=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 though the same plating is used, 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 above, because the uneven shape of the substrate is the same, when the brightness difference between hexavalent chromium and trivalent chromium is expressed as ΔL, the stopcock is 0.35 and the spout is 0.39, so there is almost no difference. By clarifying the standards, it is possible to accurately grasp the color differences of plating. The intended product is a plumbing fixture such as a water outlet, a water outlet pipe, a stop valve, and a handle, but the invention can also be applied to parts and products used in household appliances, not just plumbing fixtures.

[0038] [Hexavalent chromium plating film and its manufacturing method] 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.

[0039] Examples of the known hexavalent chromium plating method and the known hexavalent chromium plating solution include the method and plating solution described in Non-Patent Document 1 below (e.g., particularly, the description on page 91, "3.3.2 Hexavalent chromium bath composition and working conditions"). [Non-patent document 1] Electroplating Research Society: Plating Textbook, published by Nikkan Kogyo Shimbun (1986)

[0040] The hexavalent chromium plating method may be, for example, a known electrolytic method, etc. Specific examples include plating conditions disclosed in the comparative examples described below. An example of the hexavalent chromium plating solution is an electrolytic solution called a Sargent bath, which is prepared 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 amount of chromic acid. The substrate for hexavalent chromium plating to be compared with the present disclosure may be an object of a similar shape to the substrate for trivalent chromium plating of the present disclosure, or may simply be a flat object such as a test piece. The substrate for hexavalent chromium plating may be a substrate made of the same material as the substrate for trivalent chromium plating of the present disclosure, or may be made of a similar material or a different material. It is preferable that the substrate for hexavalent chromium plating has the same material for at least the outermost chromium plating layer and the layers below it. The object to be plated with hexavalent chromium plating, which is the object of comparison in the present disclosure, may have the same shape, the same base material, and the same layer structure as the object to be plated with trivalent chromium plating in the present disclosure. For example, the layer structure may be as follows, depending on the material of the object to be plated. For example, when a copper alloy is used as the base material, nickel plating is applied to the base material, and hexavalent chromium plating is provided as the outermost layer on top of that. When zinc or a zinc alloy is used as the base material, copper plating is applied to the base material, nickel plating is applied on top of that, and then hexavalent chromium plating is provided as the outermost layer. When a resin base material is used as the base material, the base material 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 on top of that, and hexavalent chromium plating is provided as the outermost layer. From the viewpoint of providing a trivalent chromium plating product having a glossy appearance equivalent to that of conventional hexavalent chromium plating, the "conventional hexavalent chromium plating film" of the present disclosure may have a thickness similar to that of a hexavalent chromium plating film commonly used in practice. That is, the 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 thickness of 0.1 to 0.5 μm, or may have a thickness of 0.3 μm.

[0041] (trivalent chromium plating product) A trivalent chromium plating product according to one embodiment of the present disclosure is obtained by the above-described method for producing a trivalent chromium plating product (including each preferred embodiment). That is, it is a trivalent chromium plating product treated with trivalent chromium plating. From the viewpoint of ensuring corrosion resistance more reliably, the plating film of the trivalent chromium plating product according to this embodiment preferably has a thickness of 0.2 μm or more (based on the plating thickness test method specified in JISH8501). The thickness is more preferably 0.2 μm or more and 0.8 μm or less. The thickness is even more preferably 0.2 μm or more and 0.4 μm or less. Furthermore, from the viewpoint of cost-effectiveness of the decorative chromium plating product, the thickness of the plating film may be 1 μm or less. The plating film of the trivalent chromium plating product of this embodiment has excellent corrosion resistance. For example, in the CASS test described below, it is preferable that the corrosion resistance is RN 9.0 or higher, more preferably RN 9.3 or higher, and even more preferably RN 9.5 or higher. In this disclosure, a "trivalent chromium plating product" refers to a plated object and a trivalent chromium plating film covering the entire or partial surface of the plated object. Examples of the plated object include components and products used in home appliances, such as the spouts, outlet pipes, stop valves, and handles of faucets, and handles of 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. In theory, trivalent chromium plating films and hexavalent chromium plating films are the same chromium metal film. However, due to differences 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 film" and "hexavalent chromium plating film" are films with different properties. As described above, the trivalent chromium plating product of this embodiment can be evaluated to a certain extent based on its color characteristics, but there are still many unknowns regarding the relationship between the microstructural characteristics of the resulting product and the color characteristics, which depend on the components of the trivalent chromium plating solution, plating conditions, etc. Microstructural characteristics include, for example, components other than the Cr metal in the coating, the surface microstructure, the cross-sectional microstructure, and the structure of the metallic chromium. The relationship between these characteristics and the color characteristics remains 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.

[0042] The plating film of the above-mentioned trivalent chromium plating product preferably has a color difference ΔE from the hexavalent chromium plating film of less than 3.5, more preferably less than 2.0. The lightness difference ΔL from the hexavalent chromium plating film is preferably less than 2.0, more preferably 1.5 or less. The lightness difference ΔL may be 0.1 or more, 0.2 or more, 0.5 or more, or 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 a trivalent chromium plating product and the lightness L of the plating film of a hexavalent chromium plating product obtained using a substrate (substrate to be plated) having the same uneven shape. The appearance of the plating film of the trivalent chromium plating product of this embodiment is excellent, and the color difference ΔE with the 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 hexavalent chromium products. It is more preferable that the plating film of the trivalent chromium plating product has color characteristics of a value a of +2.0 to -2.0 and a value b of +2.0 to -2.0. As described above, the trivalent chromium plating product of this embodiment can be evaluated to a certain extent based on its color characteristics, but there are still many unknowns regarding the relationship between the microstructural characteristics of the resulting product and the color characteristics, which depend on the components of the trivalent chromium plating solution, plating conditions, etc. Microstructural characteristics include, for example, components other than the Cr metal in the coating, the surface microstructure, the cross-sectional microstructure, and the structure of the metallic chromium. The relationship between these characteristics and the color characteristics remains 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. [Example]

[0043] 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.

[0044] (Examples 1 to 7, Comparative Examples 1 and 2) Using a stop valve as the object to be plated, a trivalent chromium plating product was produced using the trivalent chromium plating solution or hexavalent chromium plating solution with 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. Stopcock: Made of brass, with a relatively uneven surface (#600 finish), a small block shape with angular recesses, and a surface area of ​​0.76 dm 2 (149g) and six pieces were taken.

[0045] [Plating Solution Compositions in Examples and Comparative Examples] <Composition of trivalent chromium plating solution> The plating solution used contains approximately 0.5 mol / L of chromium (III) sulfate or basic chromium (III) sulfate as the Cr source, saccharin as a complexing agent at a molar ratio of approximately 1 / 15 to Cr, 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. A commercially available plating solution with similar components, Sutec 883XT (manufactured by Surtec MMC Japan Co., Ltd.), may also be used.

[0046] <Composition of hexavalent chromium plating solution> The hexavalent chromium plating solution used was an electrolytic solution generally known as a Sargent bath. Specifically, an aqueous solution containing 230g / L of industrial chromic acid was added with 0.92g / L of sulfuric acid, which is the primary catalyst and is 1 / 250 of the amount of chromic acid.

[0047] The electrode distance, stirring, CASS test, and evaluation methods for appearance and color tone listed in Table 1 are explained below.

[0048] <Electrode distance> Figures 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.

[0049] The object to be plated is immersed in the solution of the plating tank so that it is positioned between two anodes. Then, the object to be plated is plated by passing an electric 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.

[0050] As shown in the principle diagrams of Figures 2 and 3, the effect on the coating of the plating product differs depending on the ratio of the width of the objects 21 and 31 to the direction between the electrodes (horizontal direction 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 direction in Figure 1) of Figure 3 is larger, so the inter-electrode distance in Figure 3 has a greater effect on plating than Figure 2. For example, in the case of the water outlet shown in Figure 2, the outer diameter is 30 mm, the distance between electrodes (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 distance between electrodes (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 distance between the electrodes (d31, d32) is 250 mm, the position D32 closest to the electrode is 250-70m=180 mm, the position D31 farthest is 250 mm, and the ratio of these distances is 0.72. If the distance between the poles (d21, d22, d31, d32) is set to 200 mm, a shallow spout will have a distance ratio of 0.93 and will be less affected, but in the case of a bathroom faucet, the distance ratio will be 0.65, and the deeper the object to be plated, the more pronounced the difference depending on the part.

[0051] <Stirring 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 into the tube per minute. The mixing strength is 2750cm 2 The flow strength was expressed as the amount of air blown into the tube per minute. The strong stirring means that the injection rate is such that the air injection volume per minute is 15 L or more with respect to a liquid surface area of 2750 cm 2 (injection rate: 54 L / min·m 2 ). During stirring means that the injection rate is such that the air injection volume per minute is less than 10 to 15 L with respect to a liquid surface area of 2750 cm 2 (injection rate: 36 to 54 L / min·m 2 ). The weak stirring means that the injection rate is such that the air injection volume per minute is 2 or more and less than 6 L with respect to a liquid surface area of 2750 cm 2 (injection rate: 7 to 21 L / min·m 2 ).

[0052] <CASS Test> The CASS test method is described in Japanese Industrial Standard 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 to be R.N. 9 or more (corrosion area ratio exceeding 0.07% and less than or equal to 0.10%).

[0053] <Color Tone> The color of the surface of the coating of the trivalent chromium plating product and the color of the surface of the coating of the hexavalent chromium plating product were measured with a color difference meter (Color and Color Difference Meter CR - 400 (manufactured by Konica Minolta Co., Ltd.)) under the measurement conditions: SCI. The L*a*b* values in the L*a*b* color system were measured. Also, based on the color of the surface of the coating of the hexavalent chromium plating product of the same type of plated object (substrate), the color change color difference ΔE of the surface of the coating of the trivalent chromium plating product was calculated. For example, the plating products of Examples 1 to 7 and Comparative Example 2 were compared with the plating product of Comparative Example 1. Note that the hexavalent chromium plating product used as the reference was of the same type of plated object as the trivalent chromium plating product to be calculated.

[0054] <Appearance> The appearance evaluation of the plated object is performed visually. Those with some water droplet patterns on the appearance of the plated object are rated as "B". Also, when it cannot be distinguished from the appearance of the hexavalent chromium plating product, it is rated as "A".

[0055] <following around> The method for evaluating throwing power is shown in Figures 4 and 5. The ideal is full coverage, but this is affected by the shape, so it is evaluated on the product. For example, in the example of the object to be plated 41 shown in Figure 4, Cr is deposited at the corner (right-angle recess) 49, and the object is judged to pass. In other words, the throwing power is good. On the other hand, in the example of the object to be plated 51 shown in Figure 5, Cr is not deposited at the corner (right-angle recess) 59, and the object is judged to fail. In the case of Figure 5, the throwing power is insufficient.

[0056] [Table 1]

[0057] In Table 1, the meaning of each symbol is explained below. Plated object V: Water stop valve Plating solution T: trivalent chromium, H: hexavalent chromium *1:Based on theoretical calculation

[0058] <Post-processing process> The composition of the post-treatment solution is as follows: For acid immersion, an aqueous solution of a nitric acid compound can be used, and the commercially available SurTec880B (manufactured by SurTec MMC Japan Co., Ltd.) was used. Note that equivalent performance can be obtained using a 1-10 g / L aqueous solution of chromic acid. For electrolytic chromating, a method was used in which the steel was immersed in an aqueous solution of chromium phosphate or phosphoric acid, and then 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. [Explanation of symbols]

[0059] 1, 21, 31, 41: Plated object 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: Undercoat layer (nickel plating film) 48, 58: Base material 49, 59: Corner (right-angle recess) 10, 20, 30: Plating equipment D21, D31: Farthest position D22, D32: Positions closest to the electrodes d21, d22, d31, d32: Distance between poles t: length

Claims

1. A method for producing a plating product having a trivalent chromium plating film, comprising: 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; A method for producing a trivalent chromium plated product, comprising: a post-treatment step of electrolyzing or acid-immersing the plated product obtained in the plating treatment step.

2. The method for producing a trivalent chromium plated product according to claim 1, wherein the thickness of the plating film of the trivalent chromium plated product is 0.2 μm or more.

3. The method for producing a trivalent chromium plated product according to claim 1, wherein the thickness of the plating film of the trivalent chromium plated product is 0.2 to 1.0 μm.

4. The method for producing a trivalent chromium plating product according to claim 1, wherein the post-treatment time is 30 to 600 seconds.

5. The method for producing a trivalent chromium plating product according to claim 4, wherein the post-treatment time is 60 to 180 seconds.

6. In the post-treatment step, the post-treatment is performed by acid immersion, Post-treatment temperature is 50 to 90°C The method for producing a trivalent chromium plating product according to claim 1, wherein the post-treatment pH is 2.7 to 3.

3.

7. In the plating treatment step, The electrode distance for plating is 200 to 500 mm. The plating temperature is 40 to 60°C. The current density of the plating process is 5 to 10 A / dm ２ The method for producing a trivalent chromium plating product according to claim 1,

8. A trivalent chromium plating product obtained by the method for producing a trivalent chromium plating product according to any one of claims 1 to 7, 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.

9. 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 8, wherein the color characteristics are an a value of +2.0 to -2.0 and a b value of +2.0 to -2.

0.

10. The trivalent chromium plating product according to claim 8, wherein the thickness of the plating film of the trivalent chromium plating product is 0.2 μm or more and 1.0 μm or less.

11. The trivalent chromium plating product has an L value of 65 to 90, a lightness difference ΔL value from the hexavalent chromium plating film is less than 2.0, an a value of +0.5 to -1.0, and a b value of +1.0 to -1.

5. The trivalent chromium plating product according to claim 8.

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