Method for manufacturing silver-plated material, silver-coated metal sheet material, and electrical components

Abstract

To provide a silver plating material having excellent abrasion resistance and ability to maintain high peeling resistance of a silver coating layer even when exposed to a high temperature and high humidity environment.SOLUTION: The above problem is solved by a manufacturing method of a silver-plated material comprising: an electrolytic silver plating step of forming a silver coating layer on a material by electroplating using a cyanide-containing silver plating solution in which benzothiazole or derivatives thereof are dissolved; and a heat treatment step of holding the silver coating layer in a temperature range of 150 to 300°C for 3 to 30 seconds. For example, mercaptobenzothiazole or derivatives thereof can be used as substances corresponding to benzothiazole or derivatives thereof.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing silver-plated materials useful as contacts and terminal components for connectors, switches, relays, and other electrical wiring used in automobiles and consumer electronics. It also relates to a silver-coated metal sheet obtainable by this manufacturing method, and to conductive components using this silver-coated metal sheet as a material. [Background technology]

[0002] Traditionally, for connectors, switches, and other contact and terminal components, relatively inexpensive materials with excellent corrosion resistance and mechanical properties, such as copper, copper alloys, and stainless steel, have been plated with tin, silver, or gold 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 are cheaper than gold-plated materials and have the advantage of superior corrosion resistance compared to tin-plated materials.

[0003] The materials used for contacts and terminal components such as connectors and switches must also have abrasion resistance to withstand the insertion and removal of connectors and the sliding of switches. However, silver-plated materials are soft and easily abraded, so when used as materials for connection terminals, problems arise such as adhesion and adhesive wear due to insertion, removal, and sliding, or the surface being worn down during insertion of the connection terminal, increasing the coefficient of friction and thus increasing the insertion force.

[0004] The applicant disclosed in Patent Document 1 a method for obtaining a silver-plated material with superior wear resistance compared to conventional materials. 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 [Overview of the project] [Problems that the invention aims to solve]

[0006] The method disclosed in Patent Document 1 can significantly improve the wear resistance of the silver plating layer compared to conventional methods. However, it has been found that the method in Patent Document 1 has a problem in that the peel resistance of the silver coating layer to the substrate decreases when the obtained silver plating material is exposed to a harsh environment of high temperature and high humidity. Here, "silver coating layer" refers to a silver film formed on the surface of the material. For example, if a silver plating layer is formed on a silver strike plating film, the entire silver film, which is an integrated silver film of the silver strike plating film and the silver plating layer on top of it, is called the silver coating layer.

[0007] The present invention aims to provide a silver-plated material that has excellent wear resistance and maintains high peel resistance of the silver coating layer even when exposed to high temperature and high humidity environments. [Means for solving the problem]

[0008] As a result of their research, the inventors found that by subjecting a silver coating layer formed by electroplating using a silver plating solution containing benzothiazoles or their derivatives to a relatively low-temperature, short-duration heat treatment, it is possible to improve peel resistance when exposed to high-temperature, high-humidity environments while maintaining the effect of improving wear resistance.

[0009] The above objective is an electroplating process that forms a silver coating layer on a material by an electroplating method using a cyanide-containing silver plating solution in which benzothiazoles or their derivatives are dissolved, A heat treatment step of holding the silver coating layer in a temperature range of 150 to 300°C for 3 to 30 seconds, This is achieved by a method for manufacturing silver-plated materials that includes [a specific component].

[0010] The silver plating solution may contain, for example, 0.01 to 0.80 mol / L of benzothiazoles or their derivatives. The silver coating layer obtained by the electroplating process contains C and S, with a C / Ag molar ratio of, for example, 0.030 to 0.200 and an S / Ag molar ratio of, for example, 0.005 to 0.050. Examples of the benzothiazoles or their derivatives include mercaptobenzothiazoles or their derivatives.

[0011] The aforementioned material may, for example, have copper or a copper alloy as its base material. A silver strike plating film may be formed on the surface of the material. Alternatively, a nickel plating layer may be present as an underlay for the silver strike plating film.

[0012] Furthermore, the present invention provides a silver-plated metal sheet material as a specific material obtained by the above-described method for manufacturing silver-plated material, wherein a silver coating layer containing C and S, with a C / Ag molar ratio of 0.030 to 0.200 and an S / Ag molar ratio of 0.005 to 0.050, is formed on the surface of a metal sheet having copper or a copper alloy as a base material, and when subjected to the peel test described below after being held at a temperature of 85°C and a relative humidity of 85%, the silver-plated metal sheet material exhibits peel resistance such that the peeling area ratio of the silver coating layer is 3% or less. (Peel test) A stripping test is performed on all squares of the silver coating layer by making straight cuts deeper than the thickness of the silver coating layer on the surface of the silver coating layer using a cutter knife, at 3 mm intervals in two perpendicular directions. The stripping area ratio (%) is expressed as 100 × [number of squares where stripping occurred] / [total number of squares].

[0013] Furthermore, the present invention provides an electrical component that uses the above-mentioned silver-coated metal plate material as its material. [Effects of the Invention]

[0014] In the present invention, it was possible to improve the decrease in the peel resistance of the silver coating layer after exposure to a high-temperature and high-humidity environment, which was a problem with the technology of Patent Document 1. That is, according to the present invention, it was possible to provide a silver plating material excellent in both wear resistance and the peel resistance of the silver coating layer after exposure to a high-temperature and high-humidity environment.

Brief Description of the Drawings

[0015] [Figure 1] Depth-directional element concentration profile by XPS for the silver coating layer of the test material obtained in Example 2. [Figure 2] Depth-directional element concentration profile by XPS for the silver coating layer of the test material obtained in Example 6. [Figure 3] Depth-directional element concentration profile by XPS for the silver coating layer of the test material obtained in Example 7. [Figure 4] Depth-directional element concentration profile by XPS for the silver coating layer of the test material obtained in Comparative Example 1. [Figure 5] Depth-directional element concentration profile by XPS for the silver coating layer of the test material obtained in Comparative Example 3.

Modes for Carrying Out the Invention

[0016] [Electrolytic Silver Plating Process] (Silver Plating Solution) In the method for producing the silver plating material of the present invention, in the electrolytic silver plating process, an electrolytic plating method using a cyanide-containing silver plating solution is targeted. For the cyanide-containing substance and the silver-containing substance, which are the main components of the cyanide-containing silver plating solution, conventionally known ones can be applied. For example, an aqueous solution containing potassium silver cyanide or silver cyanide and potassium cyanide or sodium cyanide is preferable.

[0017] In this invention, benzothiazoles or their derivatives are used as additives to the plating solution. This is similar to the technology described in Patent Document 1. Benzothiazole (C7H5NS) is a heterocyclic compound having a benzene skeleton and a thiazole skeleton. Benzothiazoles are preferably benzothiazoles having a mercapto group (-SH), such as 2-mercaptobenzothiazole. As derivatives of benzothiazoles, 2-mercaptobenzothiazole sodium (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 2-mercaptobenzothiazole sodium (sodium mercaptobenzothiazole (SMBT)), are preferred.

[0018] Thus, when benzothiazoles such as mercaptobenzothiazole or their alkali metal salts (preferably sodium salts) are added as organic additives to a cyanide-based silver plating solution and electroplating silver, it is believed that components derived from the organic additives are incorporated into the formed silver coating layer, thereby improving wear resistance. Furthermore, it is thought that the lubricating effect of the organic additives can reduce the friction coefficient of the surface layer. This reduction in the friction coefficient suppresses adhesion due to insertion, removal, and sliding when the silver-plated material is used as a material for connectors, and this is also presumed to contribute to improved wear resistance.

[0019] The concentration of free cyanide in the silver plating solution can be set in the range of, for example, 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 by diluting the silver plating solution with water, adding potassium iodide aqueous solution, and then adding silver nitrate aqueous solution dropwise until the silver plating solution becomes cloudy, and measuring the amount added.

[0020] The concentration of benzothiazole 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.

[0021] The concentration of silver in the silver plating solution can be set in the range of, for example, 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 in the range of, for example, 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 in the range of, for example, 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 in the range of, for example, 15 to 70 g / L, and may be controlled within the range of 20 to 50 g / L.

[0022] (Silver plating conditions) Electroplating using the above silver plating solution is preferably carried out at a solution temperature of 15 to 50°C, and more preferably at 18 to 47°C. The current density for this electroplating is, for example, 0.5 to 12 A / dm². 2 It can be set within the range of 0.5~10A / dm 2 It is more preferable to do so. In order to efficiently form a good silver plating layer with few defects, 2A / dm 2 It is preferable to ensure a current density of 3A / dm 2 It is more preferable to have the above. The plating time should be set according to the application so that the average thickness of the silver plating layer formed by this electroplating is, for example, in the range of 0.5 to 10 μm, preferably 0.8 to 5 μm. In this way, a silver coating layer containing C and S can be formed, with a C / Ag molar ratio of, for example, 0.030 to 0.200 and an S / Ag molar ratio of, for example, 0.005 to 0.050.

[0023] (Plated material) Considering its application as an electrically conductive component, the material to be subjected to the above-mentioned electroplating of silver, i.e., the material to be plated, is preferably a material with a copper or copper alloy base. When the base material is copper or a copper alloy, it is preferable to use a material in which an under-plating layer, such as a nickel plating layer, is formed on the surface of the copper-based metal base material, from the viewpoint of ensuring sufficient adhesion of the silver coating layer to the base material. Furthermore, it is even more preferable to use a material in which an under-plating layer, such as a nickel plating layer, is formed on the surface of the copper-based metal base material, and a silver strike plating film is further formed on top of that under-plating layer. The thickness of the silver strike plating film is very thin, for example, about 0.001 to 0.05 μm or 0.001 to 0.02 μm, calculated from the current density and energizing time as the electrolytic deposition thickness of silver.

[0024] [Heat treatment process] As described above, electroplating silver using a silver plating solution containing benzothiazoles or their derivatives as additives can significantly improve the wear resistance of the silver coating layer. However, when the plated material is exposed to harsh operating environments of high temperature and high humidity, a phenomenon occurs in which the peel resistance of the silver coating layer decreases. When benzothiazoles or their derivatives are present in the plating layer, although the reason is not yet clear, it has been found that the adhesion of the silver coating layer decreases after being subjected to constant temperature and humidity tests (e.g., 85°C, 85% relative humidity) that consider harsh operating environments.

[0025] According to the inventors' research, by subjecting the silver coating layer obtained in the above silver plating process to a heat treatment that involves holding it for a short time in a predetermined temperature range higher than the expected operating temperature, it is possible to significantly restore the peel resistance of the silver coating layer, which had decreased immediately after the silver plating process. The excellent wear resistance of the silver coating layer is maintained even after this heat treatment. It was also found that the chemical composition of the silver coating layer does not change significantly before and after the heat treatment. The mechanism by which the peel resistance of the silver coating layer is significantly improved by heat treatment is currently unclear, but it is thought that some structure other than the composition of the silver coating layer is changed by the heat treatment.

[0026] Specifically, the silver coating layer formed by the silver plating process described above is subjected to a heat treatment in which it is held at a temperature range of 150 to 300°C for 3 to 30 seconds, more preferably 3 to 15 seconds. In this heat treatment, the maximum temperature that the silver coating layer reaches T MAX The temperature range is 150-300°C, and the temperature of the silver coating layer is above 150°C. MAX A heat pattern is adopted in which the time at which the temperature is below (°C) is in the range of 3 to 30 seconds. Maximum temperature reached T MAX If the temperature is too low, or if the holding time at 150-300°C is too short, the improvement in peel resistance may not be sufficiently achieved. Maximum temperature reached T MAX If the temperature is too high, or if the holding time at 150-300°C is too long, it will be detrimental to maintaining consistently high wear resistance. This heat treatment can be carried out in an atmospheric environment. In actual product manufacturing, the appropriate heat treatment conditions can be controlled by first determining the heat curve (temperature change over time) of the silver coating layer according to the thickness of the base material through preliminary experiments using the heating equipment to be used.

[0027] [Silver plating material] The silver-plated material obtained through the above-described silver plating and heat treatment processes according to the present invention exhibits significantly improved peel resistance of the silver coating layer when exposed to high-temperature and high-humidity environments. The composition of the silver coating layer is the same as before heat treatment, containing C and S, with a C / Ag molar ratio of, for example, 0.030 to 0.200 and an S / Ag molar ratio of, for example, 0.005 to 0.050. The C / Ag molar ratio and S / Ag molar ratio of the silver coating layer can be determined from the average concentrations of C, S, and Ag in the internal region of the silver coating layer, where the influence of contamination near the outermost surface and the influence of concentration changes near the interface with the underlying metal do not affect the elemental concentration profile in the depth direction of the silver coating layer obtained by XPS (X-ray photoelectron spectroscopy). Furthermore, the average Ag concentration in the internal region of the silver coating layer is preferably 80-95 at%, and more preferably 85 at% or higher. The average C concentration is preferably 3-15 at%. The average S concentration is preferably 0.5-5 at%.

[0028] A typical form of silver-plated material according to the present invention is a sheet material (silver-plated metal sheet material) having a silver coating layer on at least one surface of a metal sheet. The thickness of the sheet material can be, for example, 0.05 to 3.5 mm, and more preferably 0.1 to 3.0 mm. Here, "sheet 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 definition of "sheet material" as used here. Long sheets of sheet-like metal material wound into a coil are also included in the definition of "sheet material." The thickness of the sheet-like metal material is called the "sheet thickness."

[0029] Furthermore, the average thickness of the silver coating layer formed on the surface of the silver-plated material according to the present invention (or, in the case where an electroplated silver layer using the above-mentioned silver plating solution is formed on a silver strike plating film, the total average thickness of the integrated silver coating layer) is preferably set in the range of 0.5 to 10 μm, and more preferably 0.8 to 8 μm. The average crystallite diameter of the silver coating layer can be 25 nm or less, and more preferably 8 to 20 nm. The crystallite diameter of the silver coating layer can be controlled, for example, by adjusting the current density, plating solution composition, solution temperature, etc.

[0030] [Electrically Conductive Component] The above silver plating material can be processed by a known method to obtain electrically conductive components such as connectors, switches, and relays. In the electrically conductive component using the silver plating material according to the present invention, it is effective to have a structure in which the electroplated silver layer (i.e., the above-mentioned silver coating layer) having the above-described composition constitutes a portion that can be in sliding contact with the mating material.

Example

[0031] [Comparative 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, each plating was sequentially performed by the following steps to produce a silver plating material.

[0032] (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 2 and electroplating was performed for 70 seconds under these conditions to form a dull undercoat nickel plating layer on the base material. When the thickness of the undercoat nickel plating layer was measured at the central part of the surface of this plate sample using a fluorescent X-ray film thickness meter (manufactured by Hitachi High-Technologies Corporation, SFT-110A), it was about 1 μm.

[0033] (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), a plate sample with the above-mentioned underlying nickel plating layer formed thereon was used as the cathode, and a platinum-coated titanium electrode plate was used as the anode. The current density was 2.0 A / dm² at room temperature (25°C) while stirring at 500 rpm with a stirrer. 2 Electroplating was performed for 10 seconds to form a silver strike plating film. Afterwards, the silver strike plating solution was thoroughly washed away with water.

[0034] (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 (=0.16 mol / L) of 2-mercaptobenzothiazole sodium (C7H4NNaS2) as a substance corresponding to benzothiazoles or their derivatives, a plate sample on which the above-mentioned silver strike plating film has been 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 solution temperature is 35°C, and the current density is 7 A / dm². 2 A silver coating layer was formed by electroplating for 18 seconds under the specified conditions. The concentration of free cyanide in the silver plating solution was 38 g / L. The thickness of the silver coating layer at the center of the surface of this plate sample was measured using the above-mentioned X-ray fluorescence thickness meter and was found to be approximately 1 μm. In this way, a silver-plated material having silver coating layers on both sides of the plate was obtained.

[0035] The obtained silver-plated material was used as a test material and subjected to the following tests. (Constant temperature and humidity test) The test specimens were placed in a constant temperature and humidity test apparatus (TPAV-48-20, manufactured by Isuzu Manufacturing Co., Ltd.) and maintained under conditions of 85°C and 85% relative humidity. The maintenance time was set to two levels: 120 hours and 144 hours.

[0036] (Bending test) After subjecting the plate material to the constant temperature and humidity test described above, it was bent 180° by hand, then the bent portion was bent back to roughly its original shape, and the outer and inner surfaces of the bent portion were observed to check for delamination of the silver coating. In this bending test, if no delamination (detachment) or lifting of the silver coating was observed on either the outer or inner surface of the bent portion, it was rated ◎ (excellent delamination resistance). If no delamination (detachment) of the silver coating was observed on either the outer or inner surface of the bent portion, but slight lifting was observed on at least one of the silver coating layers, it was rated ○ (good delamination resistance). If delamination (detachment) of the silver coating was observed on at least one of the silver coating layers on either the outer or inner surface of the bent portion, it was rated × (poor delamination resistance). A rating of ○ or higher was judged as passing. In this example, the test material received a × rating for both levels of holding time in the constant temperature and humidity test.

[0037] (Peeling test using cross-cut peeling) For the plate material after being subjected to the constant temperature and humidity test described above, more than 100 square grids of 3 mm in diameter were formed on the surface (plated side) of the silver coating layer on both sides using a utility knife, with straight cuts deeper than the thickness of the silver coating layer made in two perpendicular directions at 3 mm intervals. A peel test was then performed using a method conforming to the peel test method using adhesive tape specified in Section 15.1 of JIS H8504:1999. The peel test using adhesive tape was performed on all grids, and the peel area ratio (%), expressed as 100 × [number of grids where peeling occurred] / [total number of grids], was calculated. A peel area ratio of 0% (no peeling) was marked with ◎, a peel area ratio exceeding 0% but 3% or less was marked with ○, and a peel area ratio exceeding 3% was marked with ×. A rating of ○ or higher was judged as passing. In this test, materials that received a rating of ○ in the 120-hour constant temperature and humidity test can be evaluated as exhibiting excellent peel resistance equivalent to or better than conventional general silver plating materials. The test material obtained in this example received a "×" rating in both levels of the constant temperature and humidity test.

[0038] (Reciprocating sliding test) Two silver-plated test materials were prepared. One was indented (inner radius = 1.5 mm) and used as an indenter, while the other was used as a flat evaluation sample. A precision sliding test apparatus (CRS-G2050-DWA, manufactured by Yamazaki Seiki Kenkyusho Co., Ltd.) was used to apply a constant load (5 N) to the evaluation sample while performing a reciprocating sliding motion (sliding distance 5 mm, sliding speed 1.67 mm / s). After this reciprocating sliding test was performed a predetermined number of times, the evaluation sample's sliding marks were observed at 100x magnification using a microscope (VHX-1000, manufactured by Keyence Corporation) to examine the wear state of the silver coating layer. In a material with a silver coating layer with a thickness of approximately 1 μm, if the copper base material is not exposed in the sliding marks after 100 reciprocating sliding cycles under these test conditions, the silver coating layer can be judged to have excellent wear resistance. Therefore, samples in which the copper of the base material was exposed in the sliding marks after 100 reciprocating sliding cycles were rated × (insufficient wear resistance), and all others were rated ○ (good wear resistance). In this example, no exposure of the copper of the base material was observed after 400 sliding cycles, and the sliding test was terminated at this stage. Since no copper exposure was observed even after 400 sliding cycles, the wear resistance was rated ○. In this case, the number of sliding cycles at which exposure of the copper of the base material occurred is indicated as "over 400" in Table 2. The manufacturing conditions for the test material are summarized in Table 1, and the investigation results are summarized in Table 2 (the same applies to each example below).

[0039] [Example 1] The silver-plated material obtained by the same silver-plating process as in Comparative Example 1 was subjected to the heat treatment process shown below.

[0040] (Heat treatment process) For this experiment, the temperature control function of a tabletop hot stirrer was used to heat-treat the silver coating layer of the plate material sample (silver-plated material) obtained in the above silver plating process. Specifically, the temperature of the tabletop hot stirrer was set to 180°C, and after the temperature stabilized at the set value, the plate material sample was placed on the flat surface of the tabletop hot stirrer, with one side of the silver coating layer of the plate material sample in close contact with the surface of the tabletop hot stirrer. Five seconds after the start of placement, the plate material sample was removed from the surface of the tabletop hot stirrer and allowed to cool in room temperature air. In other words, the placement time was 5 seconds. In this experiment, heating was performed from one side of the surface, but separate preliminary experiments measuring the heat curve showed that the temperature rose rapidly to the opposite side of the tabletop hot stirrer surface, and the maximum temperature reached of the silver coating layer on both sides T MAX Both should reach approximately the same temperature as the tabletop hot stirrer's setting temperature, and the silver coating on both sides should reach 150°C or higher. MAX It was confirmed that the time spent in the temperature range below (°C) was approximately the same as the placement time. Therefore, in this example, in both silver coating layers, the temperature range was 150°C to 180°C (T MAX The time during which the temperature is maintained below this range can be considered to be 5 seconds.

[0041] The plated material after this heat treatment process was used as the test material, and the same tests as in Comparative Example 1 were performed. As a result, the bending test and the peeling test by cross-cut peeling were both rated ◎ in both levels of holding time in the constant temperature and humidity test, and the reciprocating sliding test was rated ○. In other words, the silver coating layer after the above heat treatment achieved both excellent wear resistance and peel resistance.

[0042] [Example 2] The experiment was conducted in the same manner as in Example 1, except that the temperature of the tabletop hot stirrer was set to 200°C during the heat treatment process. As a result, the bending test and the peeling test by cross-cut peeling both received an excellent rating in both levels of the constant temperature and humidity test, and the reciprocating sliding test received a good rating. In other words, the silver coating layer after the above heat treatment achieved both excellent wear resistance and peel resistance.

[0043] [Example 3] In the heat treatment process, the experiment was conducted in the same manner as in Example 1, except that the tabletop hot stirrer was set to a temperature of 200°C and the placement time on the tabletop hot stirrer was set to 10 seconds. As a result, the bending test and the peeling test by cross-cut peeling were both rated ◎ for both levels of holding time in the constant temperature and humidity test, and the reciprocating sliding test was rated ○. In other words, the silver coating layer after the above heat treatment achieved both excellent wear resistance and peel resistance.

[0044] [Example 4] In the heat treatment process, the experiment was conducted in the same manner as in Example 1, except that the tabletop hot stirrer was set to 250°C and the constant temperature and humidity test was performed at only one level, 120 hours. As a result, the material held for 120 hours in the constant temperature and humidity test received an excellent rating in the bending test, an excellent rating in the peel test by cross-cut peeling, and a good rating in the reciprocating sliding test. In other words, the silver coating layer after the above heat treatment achieved both excellent wear resistance and peel resistance.

[0045] [Example 5] In the heat treatment process, the experiment was conducted in the same manner as in Example 1, except that the tabletop hot stirrer was set to a temperature of 160°C and the placement time on the tabletop hot stirrer was set to 20 seconds. As a result, the bending test and the peeling test by cross-cut peeling were both rated ◎ for both levels of holding time in the constant temperature and humidity test, and the reciprocating sliding test was rated ○. In other words, the silver coating layer after the above heat treatment achieved both excellent wear resistance and peel resistance.

[0046] [Example 6] The experiment was conducted in the same manner as in Example 1, except that the concentration of 2-mercaptobenzothiazole sodium (C7H4NNaS2) in the silver plating solution was set to 25 g / L (= 0.13 mol / L) in the silver plating process, the tabletop hot stirrer was set to 200°C in the heat treatment process, and the constant temperature and humidity test was performed at only one level of 120 hours. As a result, the bending test and the peel test by cross-cut peeling were both rated ◎ for the material held for 120 hours in the constant temperature and humidity test, and the reciprocating sliding test was rated ○. In other words, the silver coating layer after the above heat treatment achieved both excellent wear resistance and peel resistance.

[0047] [Example 7] The experiment was conducted in the same manner as in Example 1, except that the concentration of 2-mercaptobenzothiazole sodium (C7H4NNaS2) in the silver plating solution was set to 35 g / L (= 0.18 mol / L) in the silver plating process, the setting temperature of the tabletop hot stirrer was set to 200°C in the heat treatment process, and the constant temperature and humidity test was performed at only one level of 120 hours. As a result, the bending test and the peeling test by cross-cut peeling were both rated ◎ in the material held for 120 hours in the constant temperature and humidity test, and the reciprocating sliding test was rated ○. In other words, the silver coating layer after the above heat treatment achieved both excellent wear resistance and peel resistance.

[0048] [Example 8] The experiment was conducted in the same manner as in Example 1, except that the concentration of potassium cyanide (KCN) in the silver plating solution was set to 70 g / L in the silver plating process, the setting temperature of the tabletop hot stirrer was set to 200°C in the heat treatment process, and the constant temperature and humidity test was performed at only one level of 120 hours. The concentration of free cyanide in the silver plating solution was 28 g / L. As a result, the bending test, the peel test by cross-cut peeling, and the reciprocating sliding test of the material held for 120 hours in the constant temperature and humidity test were all rated as ○. In other words, the silver coating layer after the above heat treatment achieved both excellent wear resistance and good peel resistance.

[0049] [Example 9] The experiment was conducted in the same manner as in Example 1, except that the potassium cyanide (KCN) concentration in the silver plating solution was set to 120 g / L during the silver plating process, the tabletop hot stirrer was set to 200°C during the heat treatment process, and the constant temperature and humidity test was performed at only one level of 120 hours. The concentration of free cyanide in the silver plating solution was 48 g / L. As a result, the bending test and the peeling test by cross-cut peeling were both rated ◎ for the material held for 120 hours in the constant temperature and humidity test, and the reciprocating sliding test was rated ○. In other words, the silver coating layer after the above heat treatment achieved both excellent wear resistance and peel resistance.

[0050] [Comparative Example 2] The experiment was conducted in the same manner as in Comparative Example 1, except that the silver plating process used a silver plating solution that did not contain benzothiazoles or their derivatives, contained 37 g / L of selenium, and was performed at a solution temperature of 18°C ​​and an energizing time of 90 seconds. The concentration of free cyanide in the silver plating solution was 38 g / L. As a result, the obtained silver coating layer had a thickness of 5 μm and exhibited inferior wear resistance compared to the silver coating layer of Comparative Example 1 formed using a silver plating solution containing benzothiazoles or their derivatives.

[0051] [Comparative Example 3] In the silver plating process, a silver plating solution containing 69 g / L of selenium was used, which did not contain benzothiazoles or their derivatives, at a solution temperature of 18°C ​​and a current density of 5 A / dm². 2 The experiment was conducted in the same manner as in Comparative Example 1, except that electroplating was performed with an energizing time of 120 seconds. The concentration of free cyanide in the silver plating solution was 38 g / L. As a result, the obtained silver coating layer had a thickness of 5 μm and exhibited inferior abrasion resistance compared to the silver coating layer of Comparative Example 1, which was formed using a silver plating solution containing benzothiazoles or their derivatives.

[0052] [Comparative Example 4] In the heat treatment process, the experiment was conducted in the same manner as in Example 1, except that the tabletop hot stirrer was set to 350°C and the constant temperature and humidity test was performed at only one level, 120 hours. As a result, the bending test and the peel test by cross-cut peeling were both rated ◎ for the material held for 120 hours in the constant temperature and humidity test. However, the reciprocating sliding test was rated ×. In other words, if the heat treatment temperature is too high, the wear resistance improvement effect of using a silver plating solution containing benzothiazoles or their derivatives is impaired.

[0053] <Elemental analysis of the silver coating layer> The silver coating layer composition was analyzed using the following method for the test materials obtained in Examples 2, 6, and 7 (all with heat treatment) and the test materials obtained in Comparative Examples 1 and 3 (both without heat treatment).

[0054] From the outermost surface of the silver coating layer of the test material, elemental concentration profiles in the depth direction were measured by XPS (X-ray photoelectron spectroscopy) for C, O, S, Ag, K, Ni, and N in Examples 2, 6, 7, and Comparative Example 1, and for C, Se, S, and Ag in Comparative Example 3. Note that Se was not detected in Examples 2, 6, 7, and Comparative Example 1 (less than 0.014 at% (less than 0.01 mass%)). A PHI5000 VersaProbeIII X-ray photoelectron spectroscopy analyzer manufactured by ULVAC-PHI, Inc. was used. The measurement was performed at a maximum vacuum of 10°C. -7 The parameters are Pa, excitation source: monochromatic AlKα, output: 25W, acceleration voltage: 15kV, beam size: 100μmΦ, incident angle: 90deg, electron beam is generated by an electron neutralization gun with emission current: 20μA, bias voltage: 1.0V, and acceleration voltage: 30.0V, and ion species: Ar + The measurements were performed while irradiating with argon ions at an acceleration voltage of 0.11kV and an emission current of 7mA, with a photoelectron extraction angle of 45deg, 5 integration cycles, an integration time of 40ms (20ms x 2), a pass energy of 140eV, and a measurement energy interval of 0.25eV / step. Surface etching for depth analysis is performed using an argon ion gun, using the ion species: Ar + The measurements were performed under the following conditions: acceleration voltage: 4kV, emission current: 20mA, sweep area: 2.7mm × 2.7mm, sputtering rate: 20nm / min (SiO2 equivalent). The etching time intervals for adjusting to each measurement depth were as follows: for Examples 2, 6, and 7, the intervals were 1 minute from 0 to 20 minutes of cumulative etching time, and 0.25 minutes thereafter; for Comparative Example 1, the intervals were 2 minutes from 0 to 20 minutes of cumulative etching time, and 4 minutes thereafter; and for Comparative Example 3, the intervals were 0.1 minutes from 0 to 3 minutes of cumulative etching time, and 0.2 minutes thereafter. To determine the atomic concentrations, the peak representing the 3d orbital bond energy (Ag3d) was used for Ag, the peak representing the 1s orbital bond energy (C1s) for C, and the peak representing the 2p orbital bond energy (S2p) for S. The Shirley method was used for background processing.

[0055] Figures 1-5 illustrate the elemental concentration profiles in the depth direction obtained by XPS for the silver coating layer of each test material. Figure 1 is Example 2, Figure 2 is Example 6, Figure 3 is Example 7, Figure 4 is Comparative Example 1, and Figure 5 is Comparative Example 3.

[0056] In these elemental concentration profiles, data from the internal region of the silver coating layer, where the effects of contamination near the outermost surface and concentration changes near the interface with the underlying metal do not apply, were used. For Examples 2, 6, 7, and Comparative Example 1, the average Ag concentration, average C concentration, and average S concentration, expressed in atomic percent, were used at depths corresponding to etching times of 10 to 25 minutes, and for Comparative Example 3, at depths corresponding to etching times of 5 to 15 minutes. The average C concentration / average Ag and average S concentration / average Ag concentrations were then calculated, and these values ​​were adopted as the C / Ag molar ratio and S / Ag molar ratio of the silver coating layer for each test material. The results are shown in Table 2.

[0057] [Table 1]

[0058] Table 2

Claims

1. An electroplating process in which a silver coating layer is formed on a material by an electroplating method using a cyanide-containing silver plating solution in which benzothiazoles or their derivatives are dissolved, A heat treatment step of holding the silver coating layer in a temperature range of 150 to 300°C for 3 to 30 seconds, A method for manufacturing a silver-plated material containing silver.

2. The method for producing a silver-plated material according to claim 1, wherein the silver plating solution contains 0.01 to 0.80 mol / L of benzothiazoles or their derivatives dissolved in it.

3. A method for producing a silver-plated material according to claim 1 or 2, wherein in the electroplating silver step, a silver coating layer is formed containing C and S, with a C / Ag molar ratio of 0.030 to 0.200 and an S / Ag molar ratio of 0.005 to 0.

050.

4. A method for producing a silver-plated material according to any one of claims 1 to 3, wherein in the electroplating silver step, mercaptobenzothiazole or a derivative thereof is used as the substance corresponding to the benzothiazoles or derivative thereof.

5. The method for manufacturing a silver-plated material according to any one of claims 1 to 4, wherein the material has copper or a copper alloy as a base material.

6. The method for manufacturing a silver-plated material according to any one of claims 1 to 5, wherein the material has a silver strike plating film formed on its surface.

7. The method for manufacturing a silver-plated material according to claim 6, wherein the material has a nickel-plated layer as a base for the silver strike plating film.

8. A silver-coated metal plate material having a silver coating layer containing C and S, with a C / Ag molar ratio of 0.030 to 0.200 and an S / Ag molar ratio of 0.005 to 0.050 formed on the surface of a metal plate with a copper or copper alloy base material, wherein when subjected to the following peel test after being held at a temperature of 85°C and a relative humidity of 85%, the silver-coated metal plate material exhibits peel resistance such that the peeling area ratio of the silver coating layer is 3% or less. (Peel test) More than 100 square grids of 3 mm in diameter are formed on the surface of the silver coating layer by making straight cuts deeper than the thickness of the silver coating layer with a cutter knife in two perpendicular directions at 3 mm intervals. A peel test is performed on all grids in accordance with the peel test method using adhesive tape specified in Section 15.1 of JIS H8504:1999, and the peel area ratio (%) is defined as 100 × [number of grids where peeling occurred] / [total number of grids].

9. An electrical component using the silver-coated metal plate material described in claim 8 as the material.

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