Method for manufacturing silver-coated material

Abstract

To provide a silver coating material with good peeling resistance of a silver coating layer at a severe bend processing section, and with a good durability against micro-sliding abrasion.SOLUTION: A production method of a silver coating material includes: a lower-part silver plating step for forming a lower-part silver plated layer on a raw material using a silver plating solution excluding benzothiazoles and derivatives; an upper-part silver plating step for forming an upper-part silver plated layer on the lower-part silver plated layer by an electroplating method using a silver plating solution including one or more substances selected from among the benzothiazoles and derivatives; and a heat treatment step for holding the lower-part silver plated layer and the upper-part silver plated layer for 3-60 seconds in the temperature range of 250-400°C.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a silver coating material useful as a material for contacts such as connectors, switches, and relays used in in-vehicle and consumer electrical wiring, and terminal components, and also to a silver coating material obtainable by the manufacturing method and an energization component using the silver coating material as a material. Here, the "silver coating material" means a material on which a silver coating layer is formed. The "silver coating layer" is a layer of silver formed on the surface of the material, and includes a silver layer composed of one or more silver plating layers, and a silver layer obtained by subjecting these silver layers to heat treatment.

Background Art

[0002] Conventionally, as materials for contacts such as connectors and switches and terminal components, materials such as copper or copper alloys, stainless steel, etc., which are relatively inexpensive and have excellent corrosion resistance and mechanical properties, are plated with tin, silver, gold, etc. according to the necessary properties such as electrical properties and solderability. Among these, tin plating materials are inexpensive but inferior in corrosion resistance in high-temperature environments. Gold plating materials are excellent in corrosion resistance and have high reliability, but are costly. On the other hand, silver plating materials have the advantage of being less expensive than gold plating materials and having better corrosion resistance than tin plating materials.

[0003] Materials for contacts such as connectors and switches and terminal components are also required to have wear resistance associated with the insertion and removal of connectors and the sliding of switches. However, since silver plating materials are soft and easily worn, when using silver plating materials as materials for connection terminals, etc., adhesion and adhesive wear are likely to occur due to insertion and removal or sliding, or the surface is scraped when inserting the connection terminal, resulting in a high friction coefficient and an increase in insertion force.

[0004] The applicant of the present application has disclosed in Patent Document 1 a method for obtaining a silver plating material having better wear resistance than conventional ones. The method is to use a plating solution containing a predetermined amount of benzothiazoles or their derivatives.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2022-48959 [Summary of the Invention] [Problems 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 the prior art. However, with respect to the peel resistance of the silver plating layer in a severely bent portion or the like of the silver plating material obtained by the method of Patent Document 1, it cannot necessarily be said that it is sufficient, and it has been found that there is room for improvement. In addition, for silver-coated materials used in vibrating environments such as automotive terminals and connectors, the demand for improving durability against fretting wear is also increasing.

[0007] An object of the present invention is to provide a silver-coated material having good peel resistance of the silver coating layer in a severely bent portion and good durability against fretting wear. [Means for Solving the Problems]

[0008] As a result of investigations, the inventors have found that an object can be achieved by forming a silver plating layer into which carbon and sulfur are introduced by electroplating using a silver plating solution containing benzothiazoles or derivatives thereof on a normal silver plating layer not containing carbon or sulfur, and then constructing a modified silver coating layer derived from the multi-layer silver plating layer by heat treatment. The following inventions are disclosed in this specification.

[0009] [1] A lower silver plating step of forming a lower silver plating layer on a material using a silver plating solution not containing benzothiazoles and derivatives thereof, An upper silver plating step of forming an upper silver plating layer on the lower silver plating layer by an electroplating method using a silver plating solution containing one or more substances selected from benzothiazoles and derivatives thereof, A heat treatment step of holding the lower silver plating layer and the upper silver plating layer in a temperature range of 250 to 400°C for 3 to 60 seconds, A method for manufacturing a silver-coated material including [2] The method for manufacturing a silver-coated material according to [1] above, wherein the average thickness of the lower silver plating layer is 0.06 to 3.0 μm. [3] The method for manufacturing a silver-coated material according to [1] or [2] above, wherein the average thickness of the upper silver plating layer is 0.3 to 10.0 μm. [4] The method for manufacturing a silver-coated material according to any one of [1] to [3] above, wherein the silver plating solution used in the upper silver plating step contains at least one substance selected from benzothiazoles and their derivatives at a concentration of 0.01 to 0.80 mol / L. [5] The method for manufacturing a silver-coated material according to any one of [1] to [4] above, wherein in the upper silver plating step, at least one substance selected from benzothiazoles and their derivatives is at least one substance selected from mercaptobenzothiazoles and their derivatives. [6] The method for manufacturing a silver-coated material according to any one of [1] to [4] above, wherein in the upper silver plating step, at least one substance selected from benzothiazoles and their derivatives is at least one substance selected from benzothiazoles and their alkali metal salts. [7] The method for manufacturing a silver-coated material according to any one of [1] to [6] above, wherein the material to be subjected to the lower silver plating step has copper or a copper alloy as a base material. [8] The method for manufacturing a silver-coated material according to any one of [1] to [7] above, wherein the material to be subjected to the lower silver plating step has a nickel plating layer on the surface where the lower silver plating layer is formed. [9] The method for manufacturing a silver-coated material according to any one of [1] to [8] above, wherein the lower silver plating layer is composed of a silver strike plating layer and a silver plating layer thereon.

[10] A silver-coated material having a silver coating layer formed on the surface of a material with a copper or copper alloy substrate. In the depth-direction element concentration profile of the silver coating layer by XPS (X-ray photoelectron spectroscopy), let the cumulative sputtering time at the depth position where the atomic ratio of silver decreases to 1 / 2 of the maximum value be t0 (minutes). On the silver profile curve, let the maximum point of the atomic ratio of silver in the region where the cumulative sputtering time is less than t0 / 2 (the sample outermost surface side) be point P1, the maximum point of the atomic ratio of silver in the region where the cumulative sputtering time is greater than t0 / 2 (the sample center side) be point P2, and the minimum point of the atomic ratio of silver between point P1 and point P2 be point Q. When the ratio Ag(Q) / Ag(P1) of the atomic ratio of silver at point Q to the atomic ratio of silver at point P1 is 0.90 or less, the ratio Ag(Q) / Ag(P2) of the atomic ratio of silver at point Q to the atomic ratio of silver at point P2 is 0.90 or less, the C / Ag atomic ratio at the depth position corresponding to point Q is 0.15 or more, and the C / Ag atomic ratio at the depth position corresponding to point P2 is 0.10 or less, it is a silver-coated material.

[11] The silver-coated material according to the above

[10] , wherein the average crystallite diameter of silver in the silver coating layer is 20 nm or more.

[12] An electrical component using the silver-coated material according to the above

[10] or

[11] as a material.

[0010] In this specification, the notation "n1~n2" indicating a numerical range means "n1 or more and n2 or less". Here, n1 and n2 are numerical values satisfying n1 < n2.

Effect of the Invention

[0011] According to the present invention, it is possible to provide a silver-coated material having good peel resistance of the silver coating layer in a severe bending portion and good durability against micro-sliding wear. Therefore, the present invention contributes to improving the reliability of electrical components such as connectors used as in-vehicle components particularly exposed to vibration.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0013] FIG. 1 schematically illustrates a cross-sectional structure which is an embodiment of a material to be subjected to a heat treatment step in a method for manufacturing a silver coating material of the present invention. A lower silver plating layer 20 and an upper silver plating layer 30 are formed on a material 10. The “material” referred to here means a material corresponding to the “material to be plated” for forming the lower silver plating layer 20. In the illustrated example, the material 10 has an undercoat plating layer 2 on a base material 1.

[0014] Examples of the base material 1 include copper or a copper alloy, stainless steel, aluminum or an aluminum alloy, an iron-nickel-based alloy, a nickel-based alloy, etc. Considering the use of an electrical component, a material having copper or a copper alloy as the base material is preferable. The undercoat plating layer 2 is an effective layer for sufficiently ensuring the adhesion of the silver coating layer to the base material, and examples thereof include a plating layer made of copper, nickel, or an alloy thereof. From the viewpoint of heat resistance, a nickel plating layer is preferable.

[0015] As the lower silver plating layer 20, a silver layer without addition of carbon or sulfur (inclusion of inevitable trace amounts of carbon and sulfur is allowed) is applied. The lower silver plating layer 20 may be formed by a plurality of silver plating steps. In the illustrated example, the lower silver plating layer 20 is composed of a silver strike plating layer 3 and a silver plating layer 4 formed thereon. The silver strike plating layer 3 is an electroplated silver layer with a very thin average thickness of, for example, 0.001 to 0.05 μm, or 0.001 to 0.02 μm, and is a silver film formed as needed as a base treatment for forming the main silver plating layer. The upper silver plating layer 30 is a silver plating layer added with carbon and sulfur and can be formed by the method described later.

[0016] FIG. 2 schematically illustrates a cross-sectional structure observable by a scanning electron microscope (SEM), which is an embodiment of the material after the heat treatment step in the method for manufacturing the silver-coated material of the present invention. By the heat treatment, a silver coating layer 40 derived from each adjacent silver layer is formed. When the material having the cross-sectional structure shown in FIG. 1 is heat-treated, as shown in FIG. 2, there are an underplating layer 2 and a silver coating layer 40 on the base material 1. The silver plating layer 40 is derived from the lower silver plating layer 20 composed of the silver strike plating layer 3 and the silver plating layer 4, and the upper silver plating layer 30.

[0017] [Lower silver plating process] First, a lower silver plating layer is formed on the above-mentioned material (the material to be plated) using a silver plating solution that does not contain benzothiazoles and their derivatives. The "silver plating solution that does not contain benzothiazoles and their derivatives" is a regulation for distinguishing from the upper silver plating process described later. That is, in the lower silver plating process, a silver plating layer can be formed by a conventionally general known method. It is also possible to carry out a plurality of plating processes such as a silver strike plating process and a normal silver plating process. The amount of carbon and sulfur mixed in the lower silver plating layer is sufficiently acceptable up to the same level as that of an electroplated silver layer using a general cyanide-based silver plating solution (for example, a bright silver plating solution, a matte silver plating solution, etc.). Specifically, the concentration of one or more substances selected from benzothiazoles and their derivatives in the silver plating solution is, for example, in the range of 0.001 mol / L or less, and the C / Ag atomic ratio representing the ratio of the number of carbon atoms to silver atoms in the silver plating layer is 0.020 or less, and the S / Ag atomic ratio representing the ratio of the number of sulfur atoms to silver atoms is preferably 0.003 or less. Usually, for the formation of the silver strike plating layer and the formation of the silver plating layer thereon, an electroplating method using a cyanide-based silver plating solution may be adopted. The application of a silver plating solution using a complexing agent other than a cyanide compound is not excluded. The average thickness of the lower silver plating layer is preferably set in the range of 0.06 to 3.0 μm, and more preferably in the range of 0.1 to 1.0 μm. Considering economy, it is preferably set in the range of 0.5 times or less of the average thickness of the upper silver plating layer described later.

[0018] As a preferable plating condition for forming the main silver plating layer (the part excluding the silver strike plating and corresponding to the part numbered 4 in the example of FIG. 1) constituting the lower silver plating layer 20, the following aspects can be exemplified. For example, in a silver plating solution composed of an aqueous solution containing potassium silver cyanide (K[Ag(CN)2]) and potassium cyanide (KCN), the current density is 1 to 10 A / dm 2Electroplating can be carried out under conditions set within the range of 1 to 90 seconds of energization time. The silver plating solution can contain additive components such as brighteners (e.g., selenium) as required. The silver plating layer 4 obtained under such conditions is preferably a silver plating layer containing 99.0 mass% or more of Ag.

[0019] Note that even a silver plating layer formed using a silver plating solution that does not contain benzothiazoles and their derivatives, such as a silver film consisting only of a silver strike plating layer, which is very thin with an average thickness of 0.05 μm or less, is not considered to correspond to the "lower silver plating layer" (reference numeral 20 in the example of FIG. 1) targeted in the present invention.

[0020] [Upper silver plating step] Next, a silver plating layer containing carbon and sulfur is formed on the above-mentioned lower silver plating layer 20. In the measurement data by XPS (X-ray photoelectron spectroscopy) near the center of the thickness of the lower silver plating layer 20, it is preferable to form a silver plating layer in which the C / Ag atomic ratio representing the atomic ratio of carbon to silver is, for example, 0.050 to 0.200, and the S / Ag atomic ratio representing the atomic ratio of sulfur to silver is, for example, 0.005 to 0.050. Such an upper silver plating layer containing carbon and sulfur 30 is can be formed, for example, by the following electroplating method.

[0021] (Plating solution for the upper silver plating step) As the silver plating solution, it is preferable to use a cyanide-containing silver plating solution. For the cyanide-containing substance and silver-containing substance, which are the main components of the cyanide-containing silver plating solution, those known in the art can be applied. For example, an aqueous solution containing potassium silver cyanide (K[Ag(CN)2]) or silver cyanide (AgCN) and potassium cyanide (KCN) or sodium cyanide (NaCN) is suitable.

[0022] As an additive to the plating solution, in the present invention, one or more substances selected from benzothiazoles and their derivatives are applied. This point is the same as the technology of Patent Document 1. Benzothiazole (C7H5NS) is a heterocyclic compound having a benzene skeleton and a thiazole skeleton. The benzothiazoles are preferably benzothiazoles having a mercapto group (-SH) such as 2-mercaptobenzothiazole. As derivatives of benzothiazoles, sodium 2-mercaptobenzothiazole (sodium mercaptobenzothiazole (SMBT)), zinc-2-mercaptobenzothiazole, 5-chloro-2-mercaptobenzothiazole, 6-amino-2-mercaptobenzothiazole, 6-nitro-2-mercaptobenzothiazole, 2-mercapto-5-methoxybenzothiazole, etc. can be used. Among these derivatives of benzothiazoles, alkali metal salts of benzothiazoles are preferred, and sodium salts of benzothiazoles such as sodium 2-mercaptobenzothiazole (sodium mercaptobenzothiazole (SMBT)) are suitable.

[0023] When electroplating silver by adding benzothiazoles such as mercaptobenzothiazole or its alkali metal salt (preferably sodium salt) as an organic additive to the silver plating solution, components derived from the organic additive (components containing carbon and sulfur) are incorporated into the formed silver plating layer, and the components derived from the organic additive are contained in the silver coating layer formed by the heat treatment described later, which is considered to improve the wear resistance. Also, it is considered that the lubricating effect of the components derived from the organic additive can reduce the friction coefficient of the surface layer. The reduction of the friction coefficient exhibits an effect of suppressing the occurrence of adhesion due to insertion, extraction, or sliding when the silver coating material is used as a material for connection terminals, etc., and this is also presumed to be effective in improving the wear resistance. Since the components derived from the organic additive are contained in the silver coating layer even after the heat treatment described later, the above-mentioned wear resistance improvement effect is maintained. It is preferable to use mercaptobenzothiazole or its derivative because it facilitates the incorporation of the components of the organic additive into the silver plating layer.

[0024] The concentration of free cyanide in the silver plating solution can be set, for example, in the range of 3 to 70 g / L, more preferably 10 to 70 g / L, and even more preferably 15 to 60 g / L. The concentration of free cyanide in the silver plating solution can be determined from the dropping amount by adding an aqueous potassium iodide solution after diluting the silver plating solution with water and then dropping an aqueous silver nitrate solution until the silver plating solution becomes turbid.

[0025] The concentration of one or more substances selected from benzothiazoles and their derivatives in the silver plating solution can be set, for example, in the range of 0.01 to 0.80 mol / L, preferably 0.015 to 0.35 mol / L, more preferably 0.03 to 0.3 mol / L, and even more preferably 0.07 to 0.25 mol / L.

[0026] The concentration of silver 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 potassium silver 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, more preferably 35 to 145 g / L, and even more preferably 38 to 110 g / L. The concentration of benzothiazoles or their alkali metal salts 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.

[0027] (Silver plating conditions for the upper silver plating process) The electroplating for forming the upper silver plating layer 30 is preferably carried out at a solution temperature of 15 to 50 °C, and more preferably at a solution temperature of 18 to 47 °C. The current density of this electroplating can be set, for example, in the range of 0.5 to 12 A / dm 2 and is more preferably carried out at 0.5 to 10 A / dm 2 In order to efficiently form a good silver plating layer with few defects, 2 A / dm 2It is preferable to secure the above current density, and it is more preferable to set it to 3 A / dm 2 or more. The plating time may be set according to the application so that the average thickness of the upper silver plating layer 30 formed by this electroplated silver plating is, for example, in the range of 0.3 to 10.0 μm, more preferably 0.5 to 3.0 μm.

[0028] [Heat treatment process] As disclosed in Patent Document 1, when electroplated silver plating is performed using a silver plating solution containing benzothiazoles or their derivatives as additives, the wear resistance of the silver coating layer can be significantly improved. On the other hand, regarding the peel resistance of the silver coating layer at the location where severe bending is applied, it will be lower than that of conventional general silver plating materials. According to the study by the inventors, for the silver coating layer composed of the adjacent lower silver plating layer 20 and upper silver plating layer 30 as described above, heat treatment to performed by holding it in the temperature range of 250 to 400 °C for 3 to 60 seconds can restore the peel resistance of the silver coating layer 40 at the severe bending portion to be equal to or better than that of conventional general silver plating materials while maintaining the effect of improving wear resistance.

[0029] The lower silver plating layer 20 is a normal silver plating layer with a high silver concentration and a low carbon concentration. On the other hand, in the upper silver plating layer 30, the relative silver concentration is lower than that of the lower silver plating layer 20 due to the introduction of carbon and sulfur. When the above heat treatment is applied to the silver coating layer formed by these different silver plating layers adjacent to each other, a silver coating layer 40 with a new structure is formed by atomic diffusion. The new structure exhibits a unique silver concentration distribution where the silver concentration is high in both the region closest to the outermost surface and the region closest to the base material in the depth direction of the silver coating layer, and the silver concentration is low in the region between them. Also, the existence of a region with a high silver concentration and a low carbon concentration is maintained closer to the base material in the silver coating layer 40. Such a typical element distribution in the silver coating layer is shown in FIG. 4 described later.

[0030] The mechanism by which the silver coating layer exhibiting such an element concentration distribution overcomes the reduction in peel resistance of the silver coating layer at severe bending portions is currently unclear, but it may be affected by the presence of a region with a high silver concentration and a low carbon concentration near the base material of the silver coating layer after heat treatment.

[0031] The heat treatment conditions are such that the silver coating layer after the upper silver plating process is held in the temperature range of 250 to 400 °C for 3 to 60 seconds, more preferably 3 to 30 seconds. In this heat treatment, the maximum temperature T MAX of the silver coating layer is in the range of 250 to 400 °C, and the heat pattern is adopted such that the time during which the temperature of the silver coating layer is 250 °C or higher and Tmax (°C) or lower is in the range of 3 to 60 seconds, more preferably 3 to 30 seconds. If the maximum temperature Tmax is too low or the holding time at 250 to 400 °C is too short, the effect of improving the peel resistance of the silver coating layer at severe bending portions may not be sufficiently obtained. If the maximum temperature Tmax is too high or the holding time at 250 to 400 °C is too long, it is disadvantageous for stably maintaining high wear resistance, particularly durability against micro-sliding wear. This heat treatment can be carried out in an air atmosphere. At the actual product manufacturing site, by previously grasping the heat curve (temperature change over time) of the silver coating layer corresponding to the plate thickness of the base material in a preliminary experiment in the heating device to be used, it is possible to control the appropriate heat treatment conditions.

[0032] [Silver Coating Material] The silver coating material according to the present invention obtained through the above-described lower silver plating process, upper silver plating process, and heat treatment process has a significantly improved durability against micro-sliding wear, and the peel resistance of the silver coating layer at a site where severe bending is applied is also excellent as in a general silver plating material. As described above, in the silver coating layer, the silver concentration is high in both the region closest to the outermost surface in the depth direction and the region closest to the base material, and the silver concentration is low in the region between them. Further, carbon in the silver coating tends to concentrate closer to the center in the depth direction, and in particular, a region with a high silver concentration and a low carbon concentration is formed closer to the base material in the silver coating layer. More specifically, in the silver coating layer of the silver coating material which is a preferred embodiment of the present invention, in the depth-directional element concentration profile of the silver coating layer by XPS (X-ray photoelectron spectroscopy), the cumulative sputtering time at the depth position where the atomic ratio of silver decreases to 1 / 2 of the maximum value is taken as t0 (minutes). On the profile curve of silver, the maximum point of the atomic ratio of silver in the region where the cumulative sputtering time is less than t0 / 2 (the sample outermost surface side) is point P1, the maximum point of the atomic ratio of silver in the region where the cumulative sputtering time is greater than t0 / 2 (the sample center side) is point P2, and when the minimum point of the atomic ratio of silver between point P1 and point P2 is point Q, the ratio Ag(Q) / Ag(P1) of the atomic ratio of silver Ag(Q) at point Q to the atomic ratio of silver Ag(P1) at point P1 is 0.90 or less, the ratio Ag(Q) / Ag(P2) of the atomic ratio of silver Ag(Q) to the atomic ratio of silver Ag(P2) at point P2 is 0.90 or less, the C / Ag atomic ratio at the depth position corresponding to point Q is 0.15 or more, and the C / Ag atomic ratio at the depth position corresponding to point P2 is 0.10 or less.

[0033] Taking, as an example, FIG. 4 showing the elemental concentration profile in the depth direction of a silver coating layer obtained in Example 3 described below (heat treatment conditions: maximum temperature reached 350 ° C., holding time in the temperature range of 250 ° C. or more and the maximum temperature reached or less 10 seconds), the method for determining whether the requirements of the present invention are met will be described. In this example, the cumulative sputtering time t0 of argon at the depth position where the atomic ratio of silver decreases to 1 / 2 of the maximum value is 47 minutes, and t0 / 2 is 23.5 minutes. In FIG. 4, on the profile curve of silver, the maximum point of the atomic ratio of silver in the region where the cumulative sputtering time is less than t0 / 2 (the sample outermost surface side) is designated as P1, and the maximum point of the atomic ratio of silver in the region where the cumulative sputtering time is greater than t0 / 2 (the sample center side) is designated as P2. Further, the minimum point of the atomic ratio of silver between point P1 and point P2 is designated as Q. In this example, the ratio Ag(Q) / Ag(P1) of the atomic ratio of silver Ag(Q) at point Q to the atomic ratio of silver Ag(P1) at point P1 is 0.824, which satisfies the requirement "0.90 or less" of the present invention. The ratio Ag(Q) / Ag(P2) of Ag(Q) to the atomic ratio of silver Ag(P2) at point P2 is 0.820, which also satisfies the requirement "0.90 or less" of the present invention. The C / Ag atomic ratio at the depth position corresponding to point Q is 0.278, which satisfies the requirement "0.15 or more" of the present invention. The C / Ag atomic ratio at the depth position corresponding to point P2 is 0.054, which also satisfies the requirement "0.10 or less" of the present invention.

[0034] Further, in the silver coating material according to the present invention, it is preferable that the average crystallite size of the silver coating layer obtained by heat treatment is 20 nm or more. It is considered that since the crystal grains of silver are not excessively refined, plastic deformation of the silver plating layer is likely to occur moderately, which is particularly advantageous for improving the peel resistance at the severe bending portion of the silver coating layer containing carbon and sulfur. Although the upper limit of the average crystallite size is not particularly defined, for example, it may be 120 nm or less. The average thickness of the silver coating layer in the silver coating material according to the present invention is preferably 0.5 to 5 μm, more preferably 0.7 to 3 μm, for example, as measured by a fluorescent X-ray film thickness meter.

[0035] A typical form of the silver coating material according to the present invention is a plate material (silver-coated metal plate material) having a silver coating layer on at least one surface of a metal plate. The plate thickness can be, for example, 0.05 to 3.5 mm, and more preferably 0.1 to 3.0 mm. Here, the "plate material" means a sheet-like metal material. A thin sheet-like metal material is sometimes called "foil", and such "foil" is also included in the "plate material" referred to here. A long sheet-like metal material wound in a coil shape is also included in the "plate material". Also, the thickness of the sheet-like metal material is called the "plate thickness".

[0036] [Electrical components] The above silver coating material can be processed by a known method to obtain electrical components such as connectors, switches, and relays, and is particularly applicable to high withstand voltage components. In the electrical component using the silver coating material according to the present invention, it is effective to have a structure in which the above-described silver coating layer constitutes a portion that can be in sliding contact with the mating material.

Examples

[0037] [Example 1] (Pretreatment) As a base material, a rolled plate of 67 mm × 50 mm × 0.3 mm made of oxygen-free copper (C1020, 1 / 2H) was prepared. In an alkaline degreasing solution, this base material was used as the cathode and a stainless steel plate was used as the anode, and electrolytic degreasing was performed at a voltage of 5 V for 30 seconds. After washing the base material with water, it was pickled by immersing it in a 3% sulfuric acid aqueous solution for 15 seconds. For the base material whose surface was thus cleaned, the following steps were sequentially performed to produce a silver coating material.

[0038] (Undercoat nickel plating process) In a dull nickel plating solution composed 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 base material subjected to the pretreatment was used as the cathode, and a nickel electrode plate was used as the anode. While stirring at 500 rpm with a stirrer, the liquid temperature was 50°C and the current density was 7 A / dm 2Electroplating was performed for 70 seconds under the specified conditions to form a matte underlying nickel plating layer on the substrate. When measuring the thickness of the underlying nickel plating layer at the central part of the surface of this plate sample using a fluorescent X-ray film thickness gauge (manufactured by Hitachi High-Technologies Corporation, model SFT-110A), it was 1 μm.

[0039] (Lower silver plating process) Silver strike plating process In a silver strike plating solution composed of an aqueous solution containing 3 g / L of potassium silver cyanide (K[Ag(CN)2]) and 90 g / L of potassium cyanide (KCN), using the plate sample with the above-mentioned underlying nickel plating layer formed as the cathode and a titanium electrode plate coated with platinum as the anode, while stirring at 500 rpm with a stirrer at room temperature (25 °C), electroplating was performed at a current density of 2.0 A / dm 2 for 10 seconds to form a silver strike plating layer with an average thickness of about 0.01 μm. Then, it was washed with water to thoroughly wash away the silver strike plating solution.

[0040] Silver plating process In a silver plating solution composed of an aqueous solution containing 175 g / L of potassium silver cyanide (K[Ag(CN)2]), 95 g / L of potassium cyanide (KCN), and further containing potassium selenocyanate (KSeCN) in an amount such that the selenium concentration is 37 mg / L, using the plate sample with the above-mentioned silver strike plating layer formed as the cathode and a silver electrode plate as the anode, while stirring at 500 rpm with a stirrer, at a liquid temperature of 18 °C and a current density of 7 A / dm 2 electroplating was performed for 4 seconds under these conditions to form a silver plating layer. When measuring the thickness of the lower silver plating layer composed of the silver plating layer and the silver strike plating layer formed here at the central part of the surface of this plate sample using the above-mentioned fluorescent X-ray film thickness gauge, it was 0.2 μm.

[0041] (Upper silver plating process) An aqueous silver plating solution consisting of 175 g / L of potassium silver cyanide (K[Ag(CN)2]), 95 g / L of potassium cyanide (KCN), and 30 g / L (=0.16 mol / L) of sodium 2-mercaptobenzothiazole (C7H4NNaS2) as a substance corresponding to benzothiazoles or their derivatives. In this silver plating solution, a plate sample with the above-mentioned lower silver plating layer formed is used as the cathode, and a silver electrode plate is used as the anode. While stirring at 500 rpm with a stirrer, the liquid temperature is 35 °C and the current density is 7 A / dm 2 Electroplating was carried out for 18 seconds under the conditions of to form the upper silver plating layer. The concentration of free cyanide in the silver plating solution is 38 g / L. When the total thickness of the lower silver plating layer and the upper silver plating layer was measured at the central part of the surface of this plate sample using the above-mentioned fluorescent X-ray film thickness gauge, it was 1.2 μm. In this way, a silver-coated material having a lower silver plating layer and an upper silver plating layer on both sides of the plate was obtained. The thicknesses of each silver plating layer are shown in Table 1. The thickness of the upper silver plating layer is described as the value obtained by subtracting the measured value of the lower silver plating layer thickness from the measured value of the total thickness of the lower silver plating layer and the upper silver plating layer (the same applies in the following examples). In the case of this example, the thickness of the upper silver plating layer is 1.2 μm - 0.2 μm = 1 μm.

[0042] (Heat treatment process) Using the temperature control function of a tabletop hot stirrer, heat treatment was performed on the silver coating layer of the sheet material sample obtained in the above upper silver plating process. Specifically, the temperature of the tabletop hot stirrer was set to 300 °C. After the temperature stabilized at the set value, the sheet material sample was placed on the flat surface of the tabletop hot stirrer, and the silver coating layer on one side of the sheet material sample was brought into close contact with the surface of the tabletop hot stirrer. Thirty seconds after the start of placement, the sheet material sample was removed from the surface of the tabletop hot stirrer and allowed to cool in normal temperature air. That is, the placement time was 30 seconds. In this experiment, heating was performed from one side surface, but through measurement of the heat curve by a separate preliminary experiment, it was confirmed that the temperature rapidly increased to the surface on the opposite side of the tabletop hot stirrer, and the maximum temperature Tmax of both silver coating layers was almost equal to the set temperature of the tabletop hot stirrer, and the time during which both silver coating layers were maintained in the temperature range of 250 °C or higher and Tmax (°C) or lower was almost the same as the placement time. Therefore, in this example, it can be considered that the time during which both silver coating layers are maintained in the temperature range of 250 °C or higher and 300 °C (Tmax) or lower is 30 seconds. In this way, a silver-coated material that had completed the heat treatment process was obtained.

[0043] Using the obtained silver-coated material as a test material, the following tests were conducted. (180° Bending Test) After performing 180° bending on the sheet material that was the test material, the bent portion was bent back to approximately the original plate shape, and by observing the outer surface and the inner surface of the bent portion, it was inspected whether peeling of the silver coating layer occurred. In this test, those in which no peeling (falling off) or lifting of the silver coating layer was observed on either the outer surface or the inner surface of the bent portion were rated as ◎ (excellent peel resistance), those in which no peeling (falling off) of the silver coating layer was observed on either the outer surface or the inner surface of the bent portion, but slight lifting was observed in at least one silver coating layer were rated as ○ (good peel resistance), and those in which peeling (falling off) of the silver coating layer was observed in at least one silver coating layer on either the outer surface or the inner surface of the bent portion were rated as × (poor peel resistance). An evaluation of ○ or higher was determined to be a pass. The silver-coated material obtained in this example was rated as ◎.

[0044] (Micro-sliding Durability Test) Two silver-coated materials as test specimens were prepared. One was indented (inner R = 1.5 mm) and used as a probe, and the other was used as a flat evaluation sample. Using a precision sliding test device (manufactured by Yamazaki Seiki Kenkyusho Co., Ltd., CRS-G2050-DWA), while pressing the probe against the evaluation sample with a constant load (5 N), a reciprocating motion of micro-sliding (sliding distance 0.1 mm, sliding speed 0.2 mm / s) was continued, and the number of reciprocating sliding times when the contact resistance exceeded 0.5 mΩ was defined as the durability times of the silver coating layer. If the durability times under this condition were 3500 times or more, it could be judged that the silver coating layer had excellent wear resistance against micro-sliding. Therefore, those with durability times less than 3500 times were rated as × (resistance to micro-sliding wear: insufficient), those with durability times of 3500 times or more and less than 5000 times were rated as ○ (resistance to micro-sliding wear: good), those with durability times of 5000 times or more were rated as ◎ (resistance to micro-sliding wear: excellent), and a rating of ○ or above was judged as passing. The durability times of the silver-coated material obtained in this example were 3700 times, and it was rated as ○.

[0045] (Measurement of contact resistance) Regarding the silver coating layer on the surface of the test specimen, the contact resistance was measured using the above-mentioned precision sliding test device. As a result, the contact resistance of the silver-coated material in this example was 0.23 mΩ.

[0046] (Measurement of crystallite size) Regarding the silver coating layer of the test specimen, based on the X-ray diffraction pattern by Cu-Kα rays measured by an X-ray diffractometer (a fully automatic multi-purpose horizontal X-ray diffractometer, Smart Lab, manufactured by Rigaku Corporation), the crystallite sizes in the directions perpendicular to the (111), (200), (220), and (311) crystal planes of silver crystals were calculated respectively from the half-widths of each peak by the Scherrer formula, weighted by the orientation ratio of each crystal plane, and the average crystallite size was calculated by the weighted average of the crystallite sizes of each crystal plane. Here, the Scherrer constant was set to 0.9400. For the measurement of the half-width, the (111) peak that appears around 2θ = 38°, the (200) peak that appears around 44°, the (220) peak that appears around 64°, and the (311) peak that appears around 77° were used. As the above-mentioned orientation ratio, based on the X-ray diffraction pattern obtained by scanning the scanning range 2θ / θ using a Cu tube target and the Kβ filter method, the intensities of the X-ray diffraction peaks of the (111), (200), (220), and (311) planes of the silver plating film were divided by the respective relative intensity ratios (relative intensity ratios during powder measurement) ((111):(200):(220):(311)=100:40:25:26) described in JCPDS Card No. 40783, and the values (corrected intensities) obtained by correction were used. As a result, the average crystallite diameter of the silver coating layer in the silver coating material obtained in this example was 60.2 nm. The above results are summarized and shown in Table 1.

[0047] [Example 2] In the heat treatment step, a silver coating material was produced in the same manner as in Example 1, except that the set temperature of the desktop hot stirrer was 350 °C and the placement time on the desktop hot stirrer was 5 seconds. The silver coating material obtained in this example was evaluated as ◎ for peel resistance by the 180° bending test and also evaluated as ◎ for fretting wear resistance by the fretting fatigue test (8200 cycles of endurance). Also, the contact resistance was 0.23 mΩ, and the average crystallite diameter of the silver coating layer was 25.0 nm.

[0048] [Example 3] In the heat treatment step, a silver coating material was produced in the same manner as in Example 1, except that the set temperature of the desktop hot stirrer was 350 °C and the placement time on the desktop hot stirrer was 10 seconds. The silver coating material obtained in this example was evaluated as ◎ for peel resistance by the 180° bending test and also evaluated as ◎ for fretting wear resistance by the fretting fatigue test (10000 cycles of endurance). Also, the contact resistance was 0.18 mΩ, and the average crystallite diameter of the silver coating layer was 88.8 nm.

[0049] [Comparative Example 1] A silver coating material at the stage where the upper silver plating step was completed in the same manner as in Example 1 without performing the heat treatment step was used as the test material. The silver-coated material obtained in this example had an evaluation of × for peel resistance by the 180° bending test and an evaluation of ◎ for fretting wear resistance by the fretting durability test (6000 cycles of durability). Also, the contact resistance was 0.29 mΩ, and the average crystallite diameter of the silver coating layer was 16.6 nm. When the heat treatment is not performed, it can be seen that the peel resistance of the silver coating layer at the site where severe bending is applied is not improved.

[0050] [Comparative Example 2] A silver-coated material was produced in the same manner as in Example 1, except that only the silver strike plating layer was formed in the lower silver plating process and the formation of the main silver plating layer was omitted, and the heat treatment process was omitted. The silver-coated material obtained in this example had an evaluation of × for peel resistance by the 180° bending test and an evaluation of ○ for fretting wear resistance by the fretting durability test (4800 cycles of durability). This silver-coated material corresponds to the technology disclosed in Patent Document 1. In this case, it can be seen that the peel resistance of the silver coating layer at the site where severe bending is applied is inferior.

[0051] [Comparative Example 3] A silver-coated material was produced in the same manner as in Example 1, except that only the silver strike plating layer was formed in the lower silver plating process and the formation of the main silver plating layer was omitted, and in the heat treatment process, the set temperature of the desktop hot stirrer was 300 °C and the placement time on the desktop hot stirrer was 10 seconds. The silver-coated material obtained in this example had an evaluation of ○ for peel resistance by the 180° bending test and an evaluation of × for fretting wear resistance by the fretting durability test (1800 cycles of durability). Since the silver strike plating layer formed in this example was very thin at about 0.01 μm in average thickness, this was not regarded as the lower silver plating layer. When the lower plating layer was not formed, even if the heat treatment process was carried out, it was not possible to achieve both the improvement of the peel resistance and the fretting wear resistance at the site where severe bending was applied.

[0052] [Comparative Example 4] A silver-coated material was produced in the same manner as in Example 1, except that the lower silver plating process and the upper silver plating process were changed to the following silver plating process, and the heat treatment process was omitted.

[0053] (Silver plating process) A silver strike plating layer was formed in the same manner as in Example 1. Next, in a silver plating solution composed of an aqueous solution containing 175 g / L of potassium silver cyanide (K[Ag(CN)2]), 95 g / L of potassium cyanide (KCN), and an amount of potassium selenocyanate (KSeCN) such that the selenium concentration is 69 mg / L, a plate sample on which the above silver strike plating layer was formed was used as the cathode, a silver electrode plate was used as the anode, and while stirring at 500 rpm with a stirrer, the liquid temperature was 18 °C, the current density was 5 A / dm 2 , and electroplating was performed under the conditions of a conduction time of 120 seconds to form a silver plating layer. When the thickness of the silver coating layer composed of the silver plating layer and the silver strike plating layer formed here was measured at the central part of the surface of this plate sample using the above fluorescent X-ray film thickness meter, it was 5 μm. Since this silver coating layer is not a plating layer intended to introduce carbon or sulfur, but a known bright silver plating layer, the thickness is shown in the column of "lower silver plating layer" for convenience in Table 1 (the same applies to Comparative Example 5 described later).

[0054] The silver-coated material obtained in this example had an excellent peel resistance evaluation by a 180° bending test and a poor fretting wear resistance evaluation by a fretting fatigue test (3000 cycles). Also, the contact resistance was 0.20 mΩ, and the average crystallite diameter of the silver coating layer was 27.8 nm. It can be seen that when the silver coating layer obtained by using benzothiazoles or their derivatives in the plating solution is not present, the fretting wear resistance is inferior.

[0055] [Comparative Example 5] A silver plating solution containing potassium selenocyanate (KSeCN) in an amount such that the selenium concentration is 37 mg / L was used, and the current density during electroplating was 5 A / dm 2 to 7 A / dm 2A silver coating material was produced in the same manner as in Comparative Example 4, except that the energization time was changed from 120 seconds to 90 seconds. When the thickness of the silver coating layer composed of the silver plating layer and the silver strike plating layer formed here was measured at the center of the surface of this plate sample using the above-mentioned fluorescent X-ray film thickness meter, it was 5 μm. The silver coating material obtained in this example was evaluated as ◎ for peel resistance by a 180° bending test and evaluated as × for fretting wear resistance by a fretting durability test (1500 cycles). Also, the contact resistance was 0.18 mΩ, and the average crystallite diameter of the silver coating layer was 75.0 nm. Similar to Comparative Example 4, it can be seen from this example that when the silver coating layer obtained by using benzothiazoles or their derivatives in the plating solution is not present, the fretting wear resistance is inferior.

[0056]

Table 1

[0057] <Measurement of Element Concentration Profile of Silver Coating Layer by XPS> For reference, the measurement results of the depth-direction element concentration profiles by XPS (X-ray photoelectron spectroscopy) for the silver coating layers obtained in Comparative Example 1 (without heat treatment) and Example 3 (heat treatment conditions; maximum temperature reached 350 °C, holding time in the temperature range of 250 °C or higher and lower than the maximum temperature reached 10 seconds) are illustrated. The measurement was carried out as follows.

[0058] From the outermost surface of the silver coating layer of the test material, using XPS, for each element of C, O, S, Ag, Ni, Cu in Comparative Example 1 and C, K, O, N, S, Ag, Ni in Example 3, the element concentration profiles in the depth direction were measured respectively. As the X-ray photoelectron spectrometer, PHI5000 VersaProbeIII manufactured by ULVAC-PHI, Inc. was used. The measurement was carried out at an ultimate vacuum of 10 -7Pa, excitation source: monochromatized AlKα, output: 25 W, acceleration voltage: 15 kV, beam size 100 μmΦ, incident angle: 90 deg, emission current: 20 μA with an electron neutralization gun, bias voltage: 1.0 V, electron beam at an acceleration voltage of 30.0 V, and ion species: Ar with an argon ion gun + While irradiating with argon ions at an acceleration voltage: 0.11 kV and an emission current: 7 mA respectively, the photoelectron extraction angle: 45 deg, number of integration times: 5 times, integration time: 40 ms (20 ms × 2), pass energy: 140 eV, measurement energy interval: 0.25 eV / step were used. For surface sputtering for depth direction analysis, ion species: Ar with an argon ion gun + was carried out under the conditions of acceleration voltage: 4 kV, emission current: 20 mA, scanning area: 2.7 mm × 2.7 mm, sputtering rate: 20 nm / min (in terms of SiO2). The interval of sputtering time for adjusting each measurement depth was 1 minute interval up to a cumulative sputtering time of 20 minutes for each case, and 4 minute interval thereafter. As the spectral species for obtaining atomic concentration, the peak of the binding energy of the 3d orbital (Ag3d) of Ag, the peak of the binding energy of the 1s orbital (C1s) of C, and the peak of the binding energy of the 2p orbital (S2p) of S were used respectively, and the Shirley method was used for background processing.

[0059] Fig. 3 exemplifies the depth - direction element concentration profiles by XPS for Comparative Example 1, and Fig. 4 exemplifies those for Example 3. The points P1, P2, and Q described above are shown in the figures. Also, Table 2 summarizes the evaluations based on these depth - direction element concentration profiles.

[0060]

Table 2

Explanation of Symbols

[0061] 1 Substrate 2 Under - plating layer 3 Silver strike plating layer 4 Silver plating layer 10 Material 20 Lower silver plating layer 30 Upper silver plating layer 40 Silver coating layer

Claims

1. A lower silver plating step of forming a lower silver plating layer with an average thickness of 0.1 to 3.0 μm on a material using a silver plating solution that does not contain benzothiazoles and their derivatives; An upper silver plating step of forming an upper silver plating layer by electroplating using a silver plating solution containing one or more substances selected from benzothiazoles and their derivatives on the lower silver plating layer; A heat treatment step of holding the lower silver plating layer and the upper silver plating layer in a temperature range of 250 to 400 °C for 3 to 60 seconds; A method for manufacturing a silver-coated material including the above steps.

2. The method for manufacturing a silver-coated material according to Claim 1, wherein the average thickness of the lower silver plating layer is 0.2 to 3.0 μm.

3. The method for manufacturing a silver-coated material according to Claim 1, wherein the average thickness of the upper silver plating layer is 0.3 to 10.0 μm.

4. The method for manufacturing a silver-coated material according to Claim 1, wherein the silver plating solution used in the upper silver plating step contains one or more substances selected from benzothiazoles and their derivatives at a concentration of 0.01 to 0.80 mol / L.

5. The method for manufacturing a silver-coated material according to Claim 1, wherein in the upper silver plating step, one or more substances selected from the benzothiazoles and their derivatives are one or more substances selected from mercaptobenzothiazoles and their derivatives.

6. The method for manufacturing a silver-coated material according to Claim 1, wherein in the upper silver plating step, one or more substances selected from the benzothiazoles and their derivatives are one or more substances selected from benzothiazoles and their alkali metal salts.

7. The method for manufacturing a silver-coated material according to Claim 1, wherein the material used in the lower silver plating step has copper or a copper alloy as a base material.

8. The method for manufacturing a silver-coated material according to Claim 1, wherein the material used in the lower silver plating step has a nickel plating layer on the surface where the lower silver plating layer is formed.

9. The method for manufacturing a silver-coated material according to Claim 1, wherein the lower silver plating layer consists of a silver strike plating layer and a silver plating layer thereon.

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