Method for manufacturing silver-plated product and silver-plated product

Abstract

To provide a silver-plated material having excellent abrasion resistance and capability of keeping the peel-off resistance of its silver coating layer high, even when exposed to a high-temperature / high-humidity environment.SOLUTION: The problem is solved by a method of producing a silver-plated material using an aqueous solution, in which benzothiazole or a derivative thereof and a selenium-containing material are dissolved, with the concentration of selenium being from 0.9 to 120 mg / L and a molar ratio of selenium / benzothiazole or a derivative thereof being 0.08×10-3 or more, as a silver-plating solution upon forming a silver-plating coating layer on a material by an electric plating method using a cyan-containing silver-plating solution. Mercaptobenzothiazole or a derivative thereof, for example, can be used as a substance corresponding to benzothiazole or a derivative thereof.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a silver-plated product useful as a material for contacts and terminal parts such as connectors, switches, and relays used in electrical wiring for automobiles and consumers, and to the silver-plated product. [Background technology]

[0002] Conventionally, materials used for contacts and terminal components of connectors, switches, and the like include relatively inexpensive materials such as copper, copper alloys, and stainless steel, which are excellent in corrosion resistance and mechanical properties, and then plated with tin, silver, gold, or other metals depending on the required properties, such as electrical properties and solderability. Of these, tin-plated materials are inexpensive but have poor corrosion resistance in high-temperature environments. Gold-plated materials have excellent corrosion resistance and high reliability, but are expensive. On the other hand, silver-plated materials have the advantages of being cheaper than gold-plated materials and having better corrosion resistance than tin-plated materials.

[0003] Materials for contacts and terminal parts of connectors and switches are required to be wear-resistant due to the insertion and removal of connectors and the sliding of switches. However, because silver-plated materials are soft and easily worn, when used as materials for connection terminals, there are problems such as adhesion due to insertion and removal or sliding, which makes them prone to adhesive wear, and the surface being scraped when the connection terminal is inserted, which increases the coefficient of friction and increases the insertion force.

[0004] The present applicant has disclosed a method for obtaining a silver-plated product with better abrasion resistance than conventional methods in Patent Document 1. This method involves using a plating solution containing a predetermined amount of benzothiazoles or their derivatives. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6916971 Summary of the Invention [Problem to be solved by the invention]

[0006] According to the method disclosed in Patent Document 1, the wear resistance of the silver plating layer can be significantly improved compared to conventional methods. However, it has been found that the method of Patent Document 1 causes a problem in that the peel resistance of the silver coating layer from the substrate decreases when the obtained silver-plated product is exposed to a severe environment of high temperature and high humidity. Here, the "silver coating layer" refers to a silver film formed on the surface of a material. For example, when a silver plating layer is formed on a silver strike plating layer, the entire silver film formed by integrating the silver strike plating layer and the silver plating layer on top of it is called the silver coating layer.

[0007] An object of the present invention is to provide a silver-plated product that has excellent abrasion resistance and maintains high resistance to peeling of the silver coating layer even when exposed to a high-temperature, high-humidity environment. [Means for solving the problem]

[0008] As a result of investigations, the inventors have found that by using a silver plating solution to which a benzothiazole or a derivative thereof and a predetermined amount of selenium have been added in combination, it is possible to prevent the deterioration in peeling resistance of the silver coating layer caused by the addition of a benzothiazole or a derivative thereof.

[0009] The object of the present invention is to provide a method for forming a silver plating layer on a substrate by electroplating using a cyanide-containing silver plating solution, the method comprising dissolving a benzothiazole or its derivative and a selenium-containing substance in the silver plating solution, the selenium concentration of which is 0.9 to 120 mg / L, and a selenium / benzothiazole or its derivative molar ratio of 0.08 × 10 -3 This can be achieved by a method for producing a silver-plated product using an aqueous solution in which the molar ratio of selenium to benzothiazoles or derivatives thereof is 2.5×10 or more. -3 Over 10.0 x 10 -3 More preferably, the following is true: The benzothiazoles or derivatives thereof include, for example, mercaptobenzothiazole or derivatives thereof.

[0010] The material may have a silver underplating layer on its surface, i.e., a silver underplating layer. In particular, the material may have a nickel plating layer on a copper or copper alloy substrate, and a silver underplating layer on the nickel plating layer. The silver underplating layer in this application refers to electrolytic silver plating for underplating, known as silver strike plating.

[0011] The present invention also provides a silver-plated product having excellent abrasion resistance and peel resistance of the silver coating layer, obtained by the above-described manufacturing method. The silver-plated product has an electrolytic silver-plated layer formed on a copper or copper alloy substrate, the electrolytic silver-plated layer containing C, S, N, K, and Se, where the proportions relative to the total mass of Ag, C, S, N, K, and Se are 0.8-2.0% by mass of C, 0.5-1.5% by mass of S, 0.1-0.5% by mass of N, 0.2-1.0% by mass of K, and 0.03-0.5% by mass of Se, with a C / S molar ratio of 3.0-6.0 and an S / N molar ratio of 1.0-4.0. In this case, the copper or copper alloy substrate can be, for example, a copper or copper alloy substrate having a nickel-plated layer thereon. When such a substrate is used, the surface of the silver-plated product has a laminated structure in which a nickel-plated layer is formed on a copper or copper alloy substrate, and an electrolytic silver-plated layer having the predetermined composition is formed on the nickel-plated layer. The total content of Ag, C, S, N, K, and Se in the constituent elements of the silver plating layer is, for example, 99.0 mass % or more. The present invention also provides an electrical component using the above silver-plated product as its raw material. [Effects of the Invention]

[0012] The present invention has been able to improve the problem of the reduction in peel resistance of the silver coating layer after exposure to a high-temperature, high-humidity environment that was a problem in the technology of Patent Document 1. That is, the present invention has been able to provide a silver-plated product that is excellent in both abrasion resistance and peel resistance of the silver coating layer after exposure to a high-temperature, high-humidity environment. DETAILED DESCRIPTION OF THE INVENTION

[0013] [Silver plating solution] The method for producing a silver-plated product of the present invention is directed to an electroplating method using a cyanide-containing silver plating solution. Conventional known cyanide-containing substances and silver-containing substances, which are the main components of the cyanide-containing silver plating solution, can be used. For example, an aqueous solution containing silver potassium cyanide or silver cyanide and potassium cyanide or sodium cyanide is suitable.

[0014] In the present invention, benzothiazoles or their derivatives are used as additives to plating solutions. This is similar to the technology of Patent Document 1. Benzothiazole (CHNS) is a heterocyclic compound having a benzene skeleton and a thiazole skeleton. The benzothiazole is preferably a benzothiazole having a mercapto group (-SH), such as 2-mercaptobenzothiazole. Benzothiazole derivatives that can be used include sodium 2-mercaptobenzothiazole (sodium mercaptobenzothiazole (SMBT)), zinc-2-mercaptobenzothiazole, 5-chloro-2-mercaptobenzothiazole, 6-amino-2-mercaptobenzothiazole, 6-nitro-2-mercaptobenzothiazole, and 2-mercapto-5-methoxybenzothiazole. Among these benzothiazole derivatives, alkali metal salts of benzothiazoles are preferred, and sodium salts of benzothiazoles, such as sodium 2-mercaptobenzothiazole (sodium mercaptobenzothiazole (SMBT)), are preferred.

[0015] Thus, when electrolytic silver plating is performed using a cyanide-based silver plating solution containing an organic additive such as mercaptobenzothiazole or its alkali metal salt (preferably the sodium salt), components derived from the organic additive are incorporated into the resulting silver plating layer, improving its wear resistance. Furthermore, the lubricating effect of the organic additive is believed to reduce the coefficient of friction of the surface layer. This reduced coefficient of friction is believed to suppress adhesion due to insertion / removal and sliding when the silver-plated material is used as a material for connection terminals, etc., and is also believed to contribute to improved wear resistance.

[0016] However, when materials electroplated with a silver plating solution containing benzothiazoles or their derivatives as additives are exposed to a high-temperature, high-humidity environment, the peeling resistance of the silver coating layer decreases. When electroplating silver, it is common to form a silver strike plating layer as an undercoat prior to the final silver plating to ensure plating adhesion to the substrate. When electroplating silver in a silver plating solution containing benzothiazoles or their derivatives, even if a silver strike plating layer is formed on the undercoat, peeling of the silver coating layer (silver strike plating layer + silver plating layer) is likely to occur between the silver strike plating layer and the undercoat (e.g., nickel plating layer) after exposure to a high-temperature, high-humidity environment. Peeling resistance is particularly reduced in areas where high current density is expected. When the resulting silver-plated material is subjected to a high-temperature, high-humidity environment test and then subjected to severe bending, the problem of peeling of the silver coating layer, primarily in areas where high current density is expected, becomes apparent. Although the reason for this has not been fully elucidated, it is thought that in the high current density areas, benzothiazoles or their derivatives are formed in a crystalline state that is prone to peeling when they are incorporated, and this is thought to be the reason for the reduced adhesion of the silver coating layer after being kept at high temperature and humidity.

[0017] In the present invention, a water-soluble selenium-containing substance is used as another additive to the plating solution. That is, a benzothiazole or its derivative and a selenium-containing substance are added in combination. This has been found to significantly suppress the deterioration of the peeling resistance of the silver coating layer described above. Although the mechanism is not clear at this time, it is thought that the selenium present in the plating solution suppresses the uptake of benzothiazole or its derivative in areas with high current density, resulting in the formation of a crystalline silver that is difficult to peel. Note that the addition of Sb is not necessary to the silver plating solution used in the present invention.

[0018] The selenium concentration in the silver plating solution is preferably 0.9 to 120 mg / L, and more preferably 50 to 120 mg / L. The molar ratio of selenium to benzothiazoles or their derivatives in the silver plating solution is preferably 0.08×10 -3 It is preferable that the concentration is 2.5×10 or more. -3 Over 10.0 x 10 -3 The following ranges are more preferable.

[0019] The concentration of friesian in the silver plating solution can be set, for example, in the range of 3 to 60 g / L, more preferably 4 to 57 g / L, and even more preferably 4 to 40 g / L. The concentration of friesian in the silver plating solution can be determined by diluting the silver plating solution with water, adding an aqueous potassium iodide solution, and then dropping an aqueous silver nitrate solution until the silver plating solution becomes cloudy, and measuring the amount of the solution dropped.

[0020] The concentration of the benzothiazole component in the silver plating solution can be set, for example, in the range of 2 to 50 g / L, preferably 2.5 to 45 g / L, more preferably 5 to 40 g / L, and even more preferably 10 to 35 g / L. Here, the "benzothiazole component" refers to the portion corresponding to benzothiazole (C7H5NS) (molecular weight 135.19).

[0021] The silver concentration in the silver plating solution can be set, for example, in the range of 15 to 150 g / L, and more preferably 30 to 120 g / L. The concentration of silver potassium cyanide or silver cyanide in the silver plating solution can be set, for example, in the range of 30 to 220 g / L, and more preferably 50 to 200 g / L. The concentration of potassium cyanide or sodium cyanide in the silver plating solution can be set, for example, in the range of 30 to 150 g / L, and more preferably 35 to 145 g / L, and even more preferably 38 to 110 g / L. The concentration of benzothiazoles or alkali metal salts thereof in the silver plating solution can be set, for example, in the range of 15 to 70 g / L, and may be controlled in the range of 20 to 50 g / L. However, if the molar ratio of selenium to benzothiazoles or derivatives thereof in the silver plating solution is 0.08 × 10 as described above, -3 More preferably, 2.5 × 10 -3 Over 10.0 x 10 -3 The concentration of the benzothiazole or its alkali metal salt is set so as to fall within the following range.

[0022] [Silver plating conditions] The electrolytic silver plating using the above silver plating solution is preferably carried out at a solution temperature of 15 to 50° C., more preferably 18 to 47° C. The current density of this electrolytic silver plating is, for example, 0.5 to 10 A / dm 2 It can be set in the range of 0.5~8A / dm 2 In order to efficiently form a good silver plating layer with few defects, it is more preferable to use a current of 1.5 A / dm 2 It is preferable to ensure a current density of 2.5A / dm or more. 2 The plating time may be set depending on the application so that the average thickness of the silver plating layer obtained by electrolytic silver plating is, for example, in the range of 0.5 to 10 μm, preferably 0.8 to 8 μm, and more preferably 0.8 to 3 μm.

[0023] [Plating material] Considering the application of the silver electroplating to current-carrying components, the material to be plated is preferably a material having a copper or copper alloy base. When the base is copper or a copper alloy, it is preferable to use a material in which a base plating layer such as a nickel plating layer is formed on the surface of the copper-based metal base, from the viewpoint of ensuring sufficient adhesion of the silver coating layer to the base. It is also more preferable to use a material in which a base plating layer such as a nickel plating layer is formed on the surface of the copper-based metal base, and a base silver plating layer (silver strike plating layer) is further formed on the base plating layer.

[0024] [Silver-plated material] By electrolytic silver plating using the above plating solution, a silver-plated product can be obtained on a copper or copper alloy substrate. The electrolytic silver plating layer contains C, S, N, K, and Se, with the proportions of C: 0.8-2.0 mass%, S: 0.5-1.5 mass%, N: 0.1-0.5 mass%, K: 0.2-1.0 mass%, and Se: 0.03-0.5 mass%, based on the total mass of Ag, C, S, N, K, and Se, and has a C / S molar ratio of 3.0-6.0 and an S / N molar ratio of 1.0-4.0. An electrolytic silver plating layer with this composition exhibits excellent abrasion resistance, good adhesion to the substrate, and excellent peel resistance in bent sections. Adhesion is particularly improved when the Se content is adjusted to 0.05-0.2 mass%. The above C / S molar ratio and S / N molar ratio are achieved by incorporating components derived from the above-mentioned benzothiazoles or their derivatives into the silver plating layer. Note that this electrolytic silver plating layer may contain elements (e.g., Na, O, etc.) inevitably mixed in from the plating solution, etc., but the total content of Ag, C, S, N, K, and Se among the constituent elements of the electrolytic silver plating layer is preferably 99.0 mass% or more, more preferably 99.5 mass% or more, and even more preferably 99.8 mass% or more.

[0025] When an electrolytic silver-plated layer using the above silver plating solution is formed on a silver strike-plated layer (for example, a thickness of about 0.01 to 0.02 μm), the electrolytic silver-plated layer specified by the above composition means a silver coating layer in which the silver strike-plated layer and the electrolytic silver-plated layer using the above silver plating solution formed thereon are integrated.

[0026] The average thickness of the silver coating layer in the silver-plated product according to the present invention (when an electrolytic silver-plated layer using the above-mentioned silver plating solution is formed on the silver strike-plated layer, the total average thickness of the combined silver coating layer) is preferably set in the range of 0.5 to 10 μm, more preferably 0.8 to 8 μm, and even more preferably 0.8 to 3 μm. The average crystallite diameter of the silver coating layer in the silver-plated product according to the present invention can be 25 nm or less, more preferably 8 to 15 nm. The crystallite diameter of the silver plating layer can be controlled by adjusting, for example, the current density, plating solution composition, solution temperature, etc.

[0027] A typical form of the silver-plated product according to the present invention is a plate material having a silver-plated layer on at least one surface. The plate thickness can be, for example, 0.05 to 3.5 mm, and more preferably 0.1 to 3.0 mm. Here, "plate material" refers to a sheet-like metal material. Thin sheet-like metal materials are sometimes called "foils," and such "foils" are also included in the "plate material" referred to here. Long sheet-like metal materials wound into a coil are also included in the "plate material." The thickness of a sheet-like metal material is also referred to as "plate thickness."

[0028] [Electrical parts] The above silver-plated material can be processed by known methods to obtain current-carrying parts such as connectors, switches, relays, etc. In current-carrying parts using the silver-plated material of the present invention, it is effective to have a structure in which the electrolytic silver-plated layer having the above-mentioned composition (i.e., the above-mentioned silver coating layer) forms a part that can come into sliding contact with a mating contact material. [Example]

[0029] [Comparative Example 1] (Pretreatment) A rolled sheet of oxygen-free copper (C1020, 1 / 2H) measuring 67 mm x 50 mm x 0.3 mm was prepared as the substrate. This substrate was used as the cathode and the stainless steel plate as the anode in an alkaline degreasing solution, and electrolytic degreasing was performed at a voltage of 5 V for 30 seconds. The substrate was then rinsed with water and pickled by immersion in a 3% aqueous sulfuric acid solution for 15 seconds. The substrate, whose surface had been cleaned in this way, was then plated in the following order using the following process to produce a silver-plated product.

[0030] (Base nickel plating process) In a matte nickel plating solution consisting of an aqueous solution containing 540 g / L of nickel sulfamate tetrahydrate, 25 g / L of nickel chloride, and 35 g / L of boric acid, the pretreated substrate was used as the cathode and the nickel electrode plate as the anode, and the plating was carried out at a solution temperature of 50°C and a current density of 5 A / dm while stirring at 500 rpm with a stirrer. 2 Electroplating was performed for 80 seconds under the conditions of

[0043] , forming a matte nickel undercoat layer on the substrate. The thickness of the nickel undercoat layer was measured at the center of the surface of this sheet material sample using a fluorescent X-ray film thickness meter (SFT-110A, manufactured by Hitachi High-Tech Science Corporation) and was found to be approximately 1 μm.

[0031] (Silver strike plating process) In a silver strike plating solution consisting of an aqueous solution containing 3 g / L of potassium silver cyanide (K[Ag(CN)2]) and 90 g / L of potassium cyanide (KCN), the plate material sample on which the above-mentioned undercoat nickel plating layer was formed was used as the cathode, and a platinum-coated titanium electrode plate was used as the anode, and the plating was conducted at a current density of 2.0 A / dm at room temperature (25°C) while stirring at 500 rpm with a stirrer. 2 The plate was then subjected to electroplating at 0.5°C for 10 seconds to form a silver strike plating layer as a base layer. The plate was then rinsed with water to thoroughly wash away the silver strike plating solution.

[0032] (Silver plating process) In a silver plating solution consisting of an aqueous solution containing 175 g / L of potassium silver cyanide (K[Ag(CN)2]), 95 g / L of potassium cyanide (KCN), and 30 g / L of sodium 2-mercaptobenzothiazole (C7H4NNaS2), the plate material sample on which the above-mentioned silver strike plating base layer was formed was used as the cathode, and the silver electrode plate was used as the anode. The solution was stirred at 500 rpm with a stirrer at a solution temperature of 35°C and a current density of 7 A / dm 2 Electroplating was performed for 18 seconds under the above conditions to form a silver plating layer. The concentration of free cyan in the silver plating solution was 38 g / L, and the concentration of benzothiazole was 21 g / L. The total thickness of the base silver plating layer formed by silver strike plating and the upper silver plating layer formed thereon in this process (i.e., the thickness of the silver coating layer) at the center of the surface of this sheet material sample was measured using the fluorescent X-ray film thickness meter described above and was found to be approximately 1 μm. In this example, selenium was not added to the silver plating solution. In this way, a silver-plated product with silver coating layers on both sides of the sheet material was obtained. The plating solution composition and plating conditions for this silver plating process are shown in Table 1 (the same applies to each of the following examples). The obtained silver-plated material was used as a test material and subjected to the following tests.

[0033] (Constant temperature and humidity test) The test material was placed in a thermo-hygroscopic tester and maintained at a temperature of 85°C and a humidity of 85% for 120 hours.

[0034] (Bending test) After the constant temperature and humidity test, the plate material was bent 180° by hand, and then the bent portion was bent back to roughly the original plate shape. The outer and inner surfaces of the bent portion were observed to check whether peeling of the silver coating layer had occurred. In this bending test, samples in which peeling of the silver coating layer was not observed on either the outer or inner surface of the bent portion were rated as ○ (peel resistance: good), and others were rated × (peel resistance: poor), with a rating of ○ being judged as passing. The test material obtained in this example was rated ×.

[0035] (Cross-cut peeling test) After the constant temperature and humidity test, the silver coating layer was subjected to a more stringent peel resistance evaluation using adhesive tape, as specified in Section 15.1 of JIS H8504:1999. To meet these stringent standards, samples were prepared by cross-cutting the silver-plated surface with a utility knife. Specifically, linear cuts were made in one direction across the entire surface of one side of the test sheet, approximately 3 mm apart, and then linear cuts were made perpendicular to the cuts, approximately 3 mm apart, to form squares of approximately 3 mm squares. The adhesive tape peel test was then performed on all squares. If at least one square showed peeling of the silver coating layer, it was marked with an "X"; otherwise, it was marked with an "O." A rating of "O" in this test indicates that the silver coating layer exhibits excellent peel resistance equivalent to or better than that of conventional silver-plated materials. Even if the evaluation in this test is "x", if the evaluation in the bending test is "o", the peel resistance of the silver coating layer is evaluated as being significantly improved compared to the silver-plated material obtained by the technology of Patent Document 1, and it is thought that this will not cause any practical problems in many applications.

[0036] (Reciprocating sliding test) Two silver-plated test samples were prepared. One was indented (with an inner radius of 1.5 mm) and used as an indenter. The other was used as a flat evaluation specimen. Using a precision sliding tester (Yamazaki Seiki Kenkyusho Co., Ltd., CRS-G2050-DWA), the indenter was pressed against the evaluation specimen with a constant load (5 N) while undergoing reciprocating sliding (sliding distance: 5 mm, sliding speed: 1.67 mm / s). After the reciprocating sliding test was completed a predetermined number of times, the sliding marks on the evaluation specimen were observed at 100x magnification using a microscope (Keyence Corporation, VHX-1000) to examine the wear state of the silver coating layer. For a material with a silver coating layer approximately 1 μm thick, if the copper of the substrate was not exposed in the sliding marks after 100 reciprocating sliding cycles under these test conditions, the silver coating layer was deemed to have excellent wear resistance. Therefore, samples in which copper exposure of the substrate was observed in the sliding marks after 100 reciprocating slides were rated as × (insufficient wear resistance), and all other samples were rated as ○ (good wear resistance). In the test material of this example, no copper exposure of the substrate was observed after 200 slides, but exposure was observed after 400 slides, so the wear resistance was rated as ○. In this case, the number of slides at which copper exposure of the substrate occurred is shown in Table 2 as "more than 200 but not more than 400." The results are shown in Table 2 (the same applies to the following examples).

[0037] Comparative Example 2 An experiment was conducted under the same conditions as in Comparative Example 1, except that in the silver plating step (hereinafter simply referred to as the "silver plating step") performed after the silver strike plating step, a silver plating solution in which potassium selenocyanate was added to adjust the selenium concentration to 0.5 mg / L was used.

[0038] In the plating solution used in the silver plating step, the types and amounts of additives other than the selenium-containing substance were the same as those in Comparative Example 1 (the same applies to each of the following examples unless otherwise specified). The obtained silver-plated product failed the bending test, and the improvement in peel resistance of the silver coating layer was insufficient.

[0039] [Example 1] The experiment was carried out under the same conditions as in Comparative Example 1, except that a silver plating solution with a selenium concentration adjusted to 1.3 mg / L was used in the silver plating process. The type of selenium-containing substance used was the same as in Comparative Example 2 (the same applies in each of the following examples unless otherwise specified). The obtained silver-plated product passed the bending test, and the effect of improving the peeling resistance of the silver coating layer due to the addition of selenium to the plating solution was confirmed.

[0040] [Example 2] The experiment was carried out under the same conditions as in Comparative Example 1, except that in the silver plating step, a silver plating solution in which the selenium concentration was adjusted to 12.7 mg / L was used. The obtained silver-plated product passed the bending test, and the effect of improving the peeling resistance of the silver coating layer due to the addition of selenium to the plating solution was confirmed.

[0041] [Example 3] The experiment was carried out under the same conditions as in Comparative Example 1, except that in the silver plating step, a silver plating solution in which the selenium concentration was adjusted to 25.4 mg / L was used. The obtained silver-plated product passed the bending test, and the effect of improving the peeling resistance of the silver coating layer due to the addition of selenium to the plating solution was confirmed.

[0042] [Example 4] The experiment was carried out under the same conditions as in Comparative Example 1, except that in the silver plating step, a silver plating solution in which the selenium concentration was adjusted to 38.1 mg / L was used. The obtained silver-plated product passed the bending test and no peeling of the silver coating layer was observed in the cross-cut peeling test. In this example, the addition of selenium to the plating solution significantly improved the peel resistance of the silver coating layer.

[0043] [Example 5] The experiment was carried out under the same conditions as in Comparative Example 1, except that in the silver plating step, a silver plating solution in which the selenium concentration was adjusted to 50.8 mg / L was used. The obtained silver-plated product passed the bending test and no peeling of the silver coating layer was observed in the cross-cut peeling test. In this example, the addition of selenium to the plating solution significantly improved the peel resistance of the silver coating layer.

[0044] [Example 6] The experiment was carried out under the same conditions as in Comparative Example 1, except that in the silver plating step, a silver plating solution in which the selenium concentration was adjusted to 76.2 mg / L was used. The obtained silver-plated product passed the bending test and no peeling of the silver coating layer was observed in the cross-cut peeling test. In this example, the addition of selenium to the plating solution significantly improved the peel resistance of the silver coating layer.

[0045] [Example 7] The experiment was carried out under the same conditions as in Comparative Example 1, except that in the silver plating step, a silver plating solution in which the selenium concentration was adjusted to 101.6 mg / L was used. The obtained silver-plated product passed the bending test and no peeling of the silver coating layer was observed in the cross-cut peeling test. In this example, the addition of selenium to the plating solution significantly improved the peel resistance of the silver coating layer.

[0046] [Example 8] In the silver plating process, a silver plating solution containing 2-mercaptobenzothiazole sodium at a concentration of 25 g / L and selenium at a concentration of 71.1 mg / L was used. The solution temperature during plating was 25°C, and the current density was 3 A / dm 2 The experiment was carried out under the same conditions as in Comparative Example 1, except that the current application time was set to 43 seconds. The concentration of free cyan in the silver plating solution was 38 g / L, and the concentration of benzothiazole was 18 g / L. The obtained silver-plated product passed the bending test and no peeling of the silver coating layer was observed in the cross-cut peeling test. In this example, the addition of selenium to the plating solution significantly improved the peel resistance of the silver coating layer.

[0047] [Example 9] In the silver plating process, a silver plating solution containing 2-mercaptobenzothiazole sodium at a concentration of 25 g / L and selenium at a concentration of 71.1 mg / L was used, and the solution temperature during plating was set at 25°C and the current density at 5 A / dm 2 The experiment was carried out under the same conditions as in Comparative Example 1, except that the current application time was set to 24 seconds. The concentration of free cyan in the silver plating solution was 38 g / L, and the concentration of benzothiazole was 18 g / L. The obtained silver-plated product passed the bending test and no peeling of the silver coating layer was observed in the cross-cut peeling test. In this example, the addition of selenium to the plating solution significantly improved the peel resistance of the silver coating layer.

[0048] [Example 10] In the silver plating process, a silver plating solution containing 2-mercaptobenzothiazole sodium at a concentration of 25 g / L and selenium at a concentration of 71.1 mg / L was used, and the solution temperature during plating was set at 45°C and the current density at 5 A / dm 2 The experiment was carried out under the same conditions as in Comparative Example 1, except that the current application time was set to 24 seconds. The concentration of free cyan in the silver plating solution was 38 g / L, and the concentration of benzothiazole was 18 g / L. The obtained silver-plated product passed the bending test and no peeling of the silver coating layer was observed in the cross-cut peeling test. In this example, the addition of selenium to the plating solution significantly improved the peel resistance of the silver coating layer.

[0049] [Example 11] In the silver plating process, a silver plating solution containing 2-mercaptobenzothiazole sodium at a concentration of 35 g / L and selenium at a concentration of 71.1 mg / L was used. The solution temperature during plating was 25°C, and the current density was 3 A / dm 2 The experiment was carried out under the same conditions as in Comparative Example 1, except that the current application time was set to 43 seconds. The concentration of free cyan in the silver plating solution was 38 g / L, and the concentration of benzothiazole was 25 g / L. The obtained silver-plated product passed the bending test and no peeling of the silver coating layer was observed in the cross-cut peeling test. In this example, the addition of selenium to the plating solution significantly improved the peel resistance of the silver coating layer.

[0050] [Example 12] In the silver plating process, a silver plating solution containing 2-mercaptobenzothiazole sodium at a concentration of 35 g / L and selenium at a concentration of 71.1 mg / L was used. The solution temperature during plating was 25°C, and the current density was 5 A / dm 2 The experiment was carried out under the same conditions as in Comparative Example 1, except that the current application time was set to 24 seconds. The concentration of free cyan in the silver plating solution was 38 g / L, and the concentration of benzothiazole was 25 g / L. The obtained silver-plated product passed the bending test and no peeling of the silver coating layer was observed in the cross-cut peeling test. In this example, the addition of selenium to the plating solution significantly improved the peel resistance of the silver coating layer.

[0051] [Example 13] In the silver plating process, a silver plating solution containing 2-mercaptobenzothiazole sodium at a concentration of 35 g / L and selenium at a concentration of 71.1 mg / L was used. The solution temperature during plating was 45°C, and the current density was 3 A / dm 2 The experiment was carried out under the same conditions as in Comparative Example 1, except that the current application time was set to 43 seconds. The concentration of free cyan in the silver plating solution was 38 g / L, and the concentration of benzothiazole was 25 g / L. The obtained silver-plated product passed the bending test and no peeling of the silver coating layer was observed in the cross-cut peeling test. In this example, the addition of selenium to the plating solution significantly improved the peel resistance of the silver coating layer.

[0052] [Example 14] In the silver plating process, a silver plating solution containing 2-mercaptobenzothiazole sodium at a concentration of 35 g / L and selenium at a concentration of 71.1 mg / L was used, and the solution temperature during plating was set at 45°C and the current density at 5 A / dm 2 The experiment was carried out under the same conditions as in Comparative Example 1, except that the current application time was set to 24 seconds. The concentration of free cyan in the silver plating solution was 38 g / L, and the concentration of benzothiazole was 25 g / L. The obtained silver-plated product passed the bending test and no peeling of the silver coating layer was observed in the cross-cut peeling test. In this example, the addition of selenium to the plating solution significantly improved the peel resistance of the silver coating layer.

[0053] Comparative Example 3 The experiment was carried out under the same conditions as in Comparative Example 1, except that a silver plating solution containing neither sodium 2-mercaptobenzothiazole nor a selenium-containing substance was used in the silver plating process. The concentration of free cyan in the silver plating solution was 38 g / L, and the concentration of benzothiazole was 0 g / L. The resulting silver-plated product had poor abrasion resistance.

[0054] Comparative Example 4 An experiment was conducted under the same conditions as in Comparative Example 1, except that in the silver plating step, sodium 2-mercaptobenzothiazole was not added, and instead potassium selenocyanate was added to adjust the selenium concentration to 71.1 mg / L. The concentration of free cyan in the silver plating solution was 38 g / L, and the concentration of benzothiazole was 0 g / L. The resulting silver-plated product had poor abrasion resistance.

[0055] [Composition analysis of silver coating layer] For some comparative examples and examples, elemental analysis of the silver coating layer, which includes both the base silver plating layer formed in the silver strike plating process and the silver plating layer formed in the subsequent silver plating process, was performed as follows.

[0056] silver The weight of the silver coating layer was calculated by subtracting the weight of the sheet material sample before the silver strike plating process from the weight of the silver-plated material used as the test material. After dissolving the silver coating on the surface of the test material with nitric acid, hydrochloric acid was added until no more white precipitate of AgCl was formed. The white precipitate was filtered and washed with water, and the weight of AgCl was measured to calculate the weight of silver in the silver coating layer.

[0057] Carbon, sulfur Using a carbon / sulfur analyzer (Horiba, Ltd., EMIA-810), the silver-plated test material was heated to 1350°C in an oxygen stream and melted, and the CO and CO2 generated during the melting were qualitatively and quantitatively analyzed with an infrared detector to calculate the carbon content of the test material. Using the same method, the carbon content of the plate sample before the silver strike plating process was calculated, but was below the detection limit, so the carbon content calculated for the test material was used as the carbon content (g) in the silver coating layer. The sulfur content of the test material was calculated by qualitatively and quantitatively analyzing the SO2 generated when the silver-plated material was heated to 1350°C in an oxygen stream and melted, using an infrared detector. The sulfur content of the plate material sample before being subjected to the silver strike plating process was calculated using the same method, but was below the detection limit, so the sulfur content calculated for the test material was used as the sulfur content (g) in the silver coating layer.

[0058] nitrogen The silver-plated test material was melted in a helium stream at 5000 W using an oxygen, nitrogen, and hydrogen analyzer (manufactured by LECO Japan LLC), and the nitrogen content in the test material was calculated by quantifying the N2 generated using a thermal conductivity detector (TCD). The nitrogen content of the plate material before the silver strike plating process was calculated using the same method, but was below the detection limit, so the nitrogen content calculated for the test material was used as the nitrogen content (g) in the silver coating layer.

[0059] potassium The silver-plated test material was dissolved in nitric acid to form a liquid, and the concentration of the solution was adjusted. The potassium concentration was measured by atomic absorption spectrometry using an atomic absorption spectrophotometer (polarized Zeeman atomic absorption spectrophotometer ZA3300, manufactured by Hitachi High-Tech Science Corporation) to determine the potassium content (g) in the silver coating layer. The potassium content of the plate sample before being subjected to the silver strike plating process was calculated using the same method, and was found to be below the detection limit, so the potassium content of the test material was determined as the potassium content (g) in the silver coating layer.

[0060] selenium For test materials prepared by adding selenium to the silver plating solution, selenium analysis was also performed as follows. The silver-plated test materials were dissolved in nitric acid to form a liquid, and the concentration of the solution was adjusted. The selenium concentration was measured by plasma spectrometry using an inductively coupled plasma (ICP) optical emission spectroscopy (ICP-OES) analyzer (Seiko Instruments Inc., SPS5100) to determine the selenium content (g) in the silver coating layer. Using the same method, the selenium content of the plate samples before the silver strike plating process was calculated. Since the result was below the detection limit, the selenium content of the test materials was used as the selenium content (g) in the silver coating layer.

[0061] C / S molar ratio, S / N molar ratio The silver content (g), carbon content (g), sulfur content (g), nitrogen content (g), and potassium content (g) in the silver coating layer determined as described above, and for test materials prepared by adding selenium to the silver plating solution, the selenium content (g) were also determined as 100%, and the molar ratio of carbon to sulfur (C / S) and the molar ratio of sulfur to nitrogen (S / N) were calculated. The results of these analyses are shown in Table 2. Although this silver coating layer contains trace amounts of elements (e.g., Na, O) that are inevitably mixed in from the plating solution, the total content of Ag, C, S, N, K, and Se in the constituent elements of the silver coating layer is 99.0 mass% or more.

[0062] [Table 1]

[0063] Table 2

Claims

1. When a silver plating layer is formed on a substrate by electroplating using a cyanide-containing silver plating solution, the silver plating solution contains dissolved benzothiazoles or derivatives thereof and selenium-containing substances, and the selenium concentration is 0.9 to 120 mg / L and the molar ratio of selenium / benzothiazoles or derivatives thereof is 0.08 × 10 －３ A method for producing a silver-plated product using the above aqueous solution.

2. The molar ratio of selenium to benzothiazoles or derivatives thereof is 2.5×10 －３ Above 10.0 x 10 －３ 2. The method for producing a silver-plated product according to claim 1, wherein the following steps are performed:

3. 3. The method for producing a silver-plated product according to claim 1, wherein mercaptobenzothiazole or a derivative thereof is used as the substance corresponding to the benzothiazole or a derivative thereof.

4. The method for producing a silver-plated product according to any one of claims 1 to 3, wherein the material has a silver plating underlayer on the surface.

5. The method for producing a silver-plated product according to any one of claims 1 to 3, wherein the material has a nickel plating layer on a base material made of copper or a copper alloy, and an undercoat silver plating layer on the nickel plating layer.

6. A silver-plated product in which a silver plating layer containing C, S, N, K, and Se is formed on a material whose base material is copper or a copper alloy, wherein the silver plating layer contains, relative to the total mass of Ag, C, S, N, K, and Se, 0.8 to 2.0 mass% C, 0.5 to 1.5 mass% S, 0.1 to 0.5 mass% N, 0.2 to 1.0 mass% K, and 0.03 to 0.5 mass% Se, with a C / S molar ratio of 3.0 to 6.0 and a S / N molar ratio of 1.0 to 4.

0.

7. 7. The silver-plated product according to claim 6, wherein the material having a copper or copper alloy base has a nickel plating layer on a copper or copper alloy base.

8. 8. The silver-plated product according to claim 6, wherein the total content of Ag, C, S, N, K, and Se in the constituent elements of the silver plating layer is 99.0 mass% or more.

9. An electrical component using the silver-plated product according to any one of claims 6 to 8.

Images