CN118043503A - Method for producing silver-plated material, silver-coated metal sheet, and power-on member - Google Patents

Abstract

A silver plating material which has excellent abrasion resistance and also has a property of maintaining the peel resistance of a silver coating layer high even when exposed to a high-temperature and high-humidity environment. The above object is achieved by a method for producing a silver plating material, comprising: an electroplated silver step of forming a silver coating layer on the blank by an electroplating method using a cyanide-containing silver plating solution in which benzothiazoles or derivatives thereof are dissolved; and a heat treatment step of maintaining the silver coating layer at a temperature range of 150 to 300 ℃ for 3 to 30 seconds. As the substance belonging to the benzothiazoles or derivatives thereof, mercaptobenzothiazoles or derivatives thereof can be used, for example.

Description

Method for producing silver-plated material, silver-coated metal sheet and current-carrying part

Technical Field

The present invention relates to a method for producing a silver-plated material useful as a material for contact and terminal parts of connectors, switches, relays, etc. used in electric wiring for vehicles and people's livelihoods. In addition, it relates to a silver-coated metal plate that can be obtained by the production method, and a current-carrying part using the silver-coated metal plate as a material.

Background Art

In the past, as materials for contacts and terminal parts of connectors, switches, etc., copper, copper alloys, stainless steel, etc., which are relatively cheap and have excellent corrosion resistance and mechanical properties, are used as plating materials with tin, silver, gold, etc. according to the necessary characteristics such as electrical properties and weldability. Among these, tin-plated materials are cheap, but have poor corrosion resistance in high temperature environments. Gold-plated materials have excellent corrosion resistance and high reliability, but are expensive. On the other hand, silver-plated materials have the following advantages: they are cheaper than gold-plated materials and have excellent corrosion resistance compared to tin-plated materials.

The materials of the contacts and terminal parts of connectors and switches are also required to have wear resistance due to the plugging and unplugging of connectors and the sliding of switches. However, silver-plated materials are soft and easily wear. Therefore, if silver-plated materials are used as materials for connecting terminals, they will adhere to each other due to plugging and unplugging and sliding, and easily cause adhesion wear. This has the problem of grinding the surface when the connecting terminal is inserted, increasing the friction coefficient, and increasing the insertion force.

The applicant of the present invention discloses a method for obtaining a silver-plated material having better wear resistance than conventional materials in Patent Document 1. This method uses a plating solution containing a predetermined amount of benzothiazoles or derivatives thereof.

Prior art literature

Patent Literature

Patent Document 1: Japanese Patent No. 6916971

Summary of the invention

Problems to be solved by the invention

According to the method disclosed in Patent Document 1, the wear resistance of the silver-plated layer can be significantly improved compared with the past. However, in the method of Patent Document 1, when the obtained silver-plated material is exposed to a harsh environment of high temperature and high humidity, it is known that the problem of reduced peeling resistance of the silver coating layer with respect to the substrate occurs. Here, the so-called "silver coating layer" is a silver coating formed on the surface of the material. For example, when a silver-plated layer is formed on a silver strike-plated film, the entire silver coating in which the silver strike-plated film and the silver-plated layer thereon are integrated is referred to as a silver coating layer.

An object of the present invention is to provide a silver-plated material having excellent wear resistance and the ability to maintain high peeling resistance of a silver coating layer even when exposed to a high-temperature and high-humidity environment.

Means for solving problems

As a result of research by the inventors, it was found that by subjecting the silver coating layer formed by electroplating using a silver plating solution containing benzothiazoles or their derivatives to a relatively low temperature and short time heat treatment, it is possible to improve the peeling resistance when exposed to a high temperature and high humidity environment while maintaining the effect of improving the wear resistance.

The above object is achieved by a method for producing a silver-plated material, which comprises: forming a silver coating layer on a blank by an electroplating method using a cyanide-containing silver plating solution in which benzothiazoles or derivatives thereof are dissolved; and

A heat treatment step of maintaining the silver coating layer at a temperature range of 150 to 300° C. for 3 to 30 seconds.

As for the silver plating solution, a benzothiazole or a derivative thereof, for example, a liquid dissolved at 0.01 to 0.80 mol/L can be used. The silver coating layer obtained by the electroplating silver process contains C and S, and the C/Ag molar ratio is, for example, 0.030 to 0.200, and the S/Ag molar ratio is, for example, 0.005 to 0.050. As the benzothiazole or a derivative thereof, for example, mercaptobenzothiazole or a derivative thereof can be cited.

As for the blank, for example, a blank having a base material of copper or copper alloy is used. A silver strike film may be formed on the surface of the blank. In addition, a nickel plating layer may be provided as a base of the silver strike film.

In addition, in the present invention, as a specific material obtained by the above-mentioned method for producing a silver-plated material, there is provided a silver-coated metal sheet material, wherein a silver coating layer containing C and S and having a C/Ag molar ratio of 0.030 to 0.200 and a S/Ag molar ratio of 0.005 to 0.050 is formed on the surface of a metal plate having a base material of copper or a copper alloy, and when the silver-coated metal sheet material is subjected to the following peeling test after being kept for 120 hours under the conditions of a temperature of 85° C. and a relative humidity of 85%, the peeling area ratio of the silver coating layer is 3% or less.

(Peel test)

A linear cut deeper than the thickness of the silver coating layer was made on the surface of the silver coating layer at intervals of 3 mm in two orthogonal directions using a cutting knife, thereby forming more than 100 3 mm square grids. For all the grids, a peeling test was carried out using the method for the peeling test using an adhesive tape specified in Item 15.1 of JIS H8504:1999, and the value represented by 100×[number of grids where peeling occurred]/[total number of grids] was set as the peeling area ratio (%).

Furthermore, the present invention provides a current-carrying component using the silver-coated metal sheet material as a material.

More specifically, the following inventions are disclosed in this specification.

[1] A method for producing a silver-plated material, comprising: forming a silver coating layer on a blank by electroplating using a cyanide-containing silver plating solution in which benzothiazoles or derivatives thereof are dissolved; and

A heat treatment step of maintaining the silver coating layer at a temperature range of 150 to 300° C. for 3 to 30 seconds.

[2] The method for producing a silver-plated material according to [1] above, wherein the silver-plating solution is a solution in which benzothiazole or a derivative thereof is dissolved at 0.01 to 0.80 mol/L.

[3] A method for producing a silver-plated material according to [1] or [2] above, wherein in the electroplating silver step, a silver coating layer containing C and S with a C/Ag molar ratio of 0.030 to 0.200 and a S/Ag molar ratio of 0.005 to 0.050 is formed.

[4] A method for producing a silver-plated material according to any one of [1] to [3] above, wherein in the electro-silver plating step, mercaptobenzothiazole or a derivative thereof is used as a substance belonging to the benzothiazole class or a derivative thereof.

[5] The method for producing a silver-plated material according to any one of [1] to [4] above, wherein the base material of the blank has copper or a copper alloy.

[6] The method for producing a silver-plated material according to any one of [1] to [5] above, wherein a silver strike plating film is formed on the surface of the blank.

[7] The method for producing a silver-plated material according to [6] above, wherein the blank has a nickel-plated layer as a base of the silver strike-plated film.

[8] A silver-coated metal sheet, wherein a silver coating layer containing C and S and having a C/Ag molar ratio of 0.030 to 0.200 and a S/Ag molar ratio of 0.005 to 0.050 is formed on the surface of a metal plate having a base material of copper or a copper alloy, and wherein the silver-coated metal sheet exhibits peeling resistance such that the peeling area ratio of the silver coating layer becomes 3% or less when subjected to the following peeling test after being kept for 120 hours under conditions of a temperature of 85° C. and a relative humidity of 85%,

(Peel test)

A linear cut deeper than the thickness of the silver coating layer was made on the surface of the silver coating layer at intervals of 3 mm in two orthogonal directions using a cutting knife, thereby forming more than 100 3 mm square grids. For all the grids, a peeling test was carried out using the method for the peeling test using an adhesive tape specified in Item 15.1 of JIS H8504:1999, and the value represented by 100×[number of grids where peeling occurred]/[total number of grids] was set as the peeling area ratio (%).

[9] A current-carrying component, wherein the silver-coated metal sheet material according to [8] above is used as a material.

Effects of the Invention

In the present invention, the deterioration of the peeling resistance of the silver coating layer after exposure to a high temperature and high humidity environment, which is considered to be a problem in the technology of Patent Document 1, can be improved. That is, according to the present invention, a silver-plated material having excellent wear resistance and peeling resistance of the silver coating layer after exposure to a high temperature and high humidity environment can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the element concentration distribution in the depth direction of the silver coating layer of the test material obtained in Example 2 using XPS.

FIG. 2 is a graph showing the element concentration distribution in the depth direction of the silver coating layer of the test material obtained in Example 6 using XPS.

FIG. 3 is a graph showing the element concentration distribution in the depth direction of the silver coating layer of the test material obtained in Example 7 using XPS.

FIG. 4 is a graph showing the element concentration distribution in the depth direction of the silver coating layer of the test material obtained in Comparative Example 1 using XPS.

FIG. 5 is a graph showing the element concentration distribution in the depth direction of the silver coating layer of the test material obtained in Comparative Example 3 using XPS.

DETAILED DESCRIPTION

[Silver plating process]

(Silver plating solution)

In the manufacturing method of the silver-plated material of the present invention, in the electroplating silver process, the electroplating method using a cyanide-containing silver plating solution is used as the object. Regarding the cyanide-containing substance and the silver-containing substance as the main component of the cyanide-containing silver plating solution, the substances known in the past can be applied. For example, it is preferable to contain an aqueous solution of potassium silver cyanide or silver cyanide, and potassium cyanide or sodium cyanide.

As an additive in the plating solution, in the present invention, benzothiazoles or derivatives thereof are used. This is the same as the technology of Patent Document 1. Benzothiazole (C ₇ H ₅ NS) 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. In addition, 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, for example, sodium salts of benzothiazoles such as sodium 2-mercaptobenzothiazole (sodium mercaptobenzothiazole (SMBT)) are preferred.

In this way, it is believed that if benzothiazoles such as mercaptobenzothiazole or alkali metal salts thereof (preferably sodium salt) are added as organic additives in the cyanide silver plating solution for electroplating silver, the components from the organic additives are collected in the formed silver coating layer, and the wear resistance is improved. In addition, it is believed that the friction coefficient of the surface layer can be reduced by utilizing the lubricating effect of the organic additive. It is speculated that by reducing the friction coefficient, when the silver-plated material is used as a material for the connection terminal, the occurrence of adhesion caused by plugging and unplugging and sliding is suppressed, which also contributes to the improvement of wear resistance.

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 by diluting the silver plating solution with water, adding an aqueous potassium iodide solution, and dripping an aqueous silver nitrate solution until the silver plating solution becomes cloudy.

The concentration of the benzothiazole component in the silver plating solution can be set in the range of, for example, 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 further preferably 0.07 to 0.25 mol/L.

The concentration of silver in the silver plating solution can be set in the range of, for example, 15 to 150 g/L, and is more preferably set to 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 is more preferably set to 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, and is more preferably set to 35 to 145 g/L, and is further preferably set to 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 can be managed to a range of 20 to 50 g/L.

(Silver plating conditions)

The electroplating of silver using the above-mentioned silver plating solution is preferably carried out at a liquid temperature of 15 to 50° C., and more preferably at a liquid temperature of 18 to 47° C. The current density of the electroplating of silver can be set in the range of 0.5 to 12 A/dm ² , for example, and is more preferably carried out at 0.5 to 10 A/dm ^2. In order to efficiently form a good silver-plated layer with few defects, it is preferred to ensure a current density of 2 A/dm ² or more, and more preferably 3 A/dm ² or more. The plating time can be set according to the application so that the average film thickness of the silver-plated layer formed by the electroplating of silver becomes, 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 with a C/Ag molar ratio of, for example, 0.030 to 0.200 and a S/Ag molar ratio of, for example, 0.005 to 0.050 can be formed.

(Plating blank)

As the blank for the above-mentioned electroplated silver, i.e., the plated material, if the use of the current-carrying parts is taken into consideration, a material with copper or copper alloy as the base material is preferably used. In the case where the base material is copper or copper alloy, from the viewpoint of fully ensuring the adhesion of the silver coating layer to the base material, it is preferred to use a blank having a base plating layer such as a nickel plating layer formed on the surface of the copper-based metal as the base material. In addition, it is more preferred to use a blank having a base plating layer such as a nickel plating layer formed on the surface of the copper-based metal as the base material, and a silver strike plating film further formed on the base plating layer. The thickness of the silver strike plating film is represented by the electrolytic deposition film thickness of silver calculated from the current density and the current-carrying time, for example, about 0.001 to 0.05 μm or 0.001 to 0.02 μm, which is very thin.

[Heat treatment process]

As described above, if silver plating is performed using a silver plating solution using benzothiazoles or their derivatives as additives, the wear resistance of the silver coating layer can be significantly improved. However, if the plated material is exposed to a harsh use environment of high temperature and high humidity, the peeling resistance of the silver coating layer decreases. When benzothiazoles or their derivatives are present in the plating layer, the reason is unclear, but it is known that the adhesion of the silver coating layer after a constant temperature and humidity test (e.g., 85°C, relative humidity 85%) considering the harsh use environment is reduced.

According to the inventor's research, the silver coating obtained in the above-mentioned silver plating process is subjected to a heat treatment for a short time in a specified temperature range higher than the expected use temperature, so that the peeling resistance of the silver coating layer that has been reduced after the silver plating process can be significantly restored. The excellent wear resistance of the silver coating layer is also maintained after the heat treatment. In addition, it can also be known that the chemical composition of the silver coating layer does not change significantly before and after the heat treatment. It is not clear at present how the peeling resistance of the silver coating layer is significantly improved by heat treatment, but it is believed that some structures other than the composition of the silver coating layer change due to the heat treatment.

Specifically, a heat treatment is performed in which the silver coating layer formed by the above-mentioned silver plating process is maintained at a temperature range of 150 to 300°C for 3 to 30 seconds, more preferably 3 to 15 seconds. In this heat treatment, a heating mode is adopted in which the maximum reaching temperature T _MAX of the silver coating layer is in the range of 150 to 300°C, and the time when the temperature of the silver coating layer is above 150°C and below T _MAX (°C) is in the range of 3 to 30 seconds. In the case where the maximum reaching temperature T _MAX is too low, or the holding time at 150 to 300°C is too short, the effect of improving the peeling resistance may not be fully obtained. In the case where the maximum reaching temperature T _MAX is too high, or the holding time at 150 to 300°C is too long, it becomes disadvantageous in stably maintaining high wear resistance. This heat treatment can be implemented in an atmospheric atmosphere. At the actual product manufacturing site, by using a preliminary experiment in the heating device used to grasp the heating curve (temperature change over time) of the silver coating layer according to the plate thickness of the substrate in advance, it can be controlled to be an appropriate heat treatment condition.

[Silver-plated material]

As for the silver-plated material according to the present invention obtained through the above-mentioned silver plating process and heat treatment process, the peeling resistance of the silver coating layer when exposed to a high temperature and high humidity environment is significantly improved. The composition of the silver coating layer is the same as before the heat treatment, containing C and S, and the C/Ag molar ratio is, for example, 0.030 to 0.200, and the S/Ag molar ratio is, for example, 0.005 to 0.050. As for the C/Ag molar ratio and the S/Ag molar ratio of the silver coating layer, it can be obtained from the average concentration of C, S, and Ag in the internal area of the silver coating layer in the element concentration distribution in the depth direction of the silver coating layer obtained by XPS (X-ray photoelectron spectroscopy), without the influence of contamination near the outermost surface and the influence of concentration changes near the interface with the base metal.

The average Ag concentration in the inner region of the silver coating layer is preferably 80 to 95 at%, more preferably 85 at% or more. The average C concentration is preferably 3 to 15 at%, and the average S concentration is preferably 0.5 to 5 at%.

A representative form of the silver-plated material according to the present invention is a plate having a silver coating layer on at least one side of the metal plate (silver-coated metal plate). The plate thickness can be, for example, 0.05 to 3.5 mm, more preferably 0.1 to 3.0 mm. Here, "plate" means a sheet of metal material. Thin sheet metal materials are sometimes also referred to as "foils", but such "foils" are also included in the "plate" mentioned here. Sheet metal materials wound into a coil-shaped strip are also included in the "plate". In addition, the thickness of the sheet metal material is referred to as "plate thickness".

In addition, the average thickness of the silver coating layer formed on the surface of the silver-plated material according to the present invention (when the electroplated silver layer using the above-mentioned silver plating solution is formed on the silver strike plating film, the total average thickness of the silver coating layer formed by integrating them) is preferably set in the range of, for example, 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 by adjusting, for example, the current density, the composition of the plating solution, the solution temperature, etc.

[Electrified parts]

By processing the silver-plated material using a known method, current-carrying parts such as connectors, switches, and relays can be obtained. In the current-carrying parts using the silver-plated material according to the present invention, it is effective that the electroplated silver layer having the above-mentioned composition (i.e., the above-mentioned silver coating layer) has a structure that constitutes a portion that can slide with the contact object material.

Example

[Comparative Example 1]

(Pre-processing)

As a substrate, a rolled plate of 67 mm × 50 mm × 0.3 mm containing oxygen-free copper (C1020, 1/2H) was prepared. The substrate was used as a cathode in an alkaline degreasing solution, and a stainless steel plate was used as an anode. Electrolytic degreasing was performed at a voltage of 5 V for 30 seconds. After the substrate was washed with water, it was immersed in a 3% sulfuric acid aqueous solution for 15 seconds to pickle. For the substrate whose surface was cleaned in this way, each plating was performed in sequence using the steps shown below to produce a silver-plated material.

(Base nickel plating process)

In a matte nickel plating solution containing an aqueous solution of 540 g/L nickel sulfamate tetrahydrate, 25 g/L nickel chloride and 35 g/L boric acid, the pre-treated substrate was used as a cathode and the nickel electrode plate was used as an anode. Electroplating was performed for 70 seconds under the conditions of a liquid temperature of 50°C and a current density of 7 A/dm ² while stirring with a stirrer at 500 rpm to form a matte base nickel plating layer on the substrate. The thickness of the base nickel plating layer was measured at the center of the surface of the plate sample using a fluorescent X-ray film thickness meter (manufactured by Hitachi High-Technologies Corporation, SFT-110A), and the result was about 1 μm.

(Silver strike plating process)

In a silver strike plating solution containing 3 g/L of potassium silver cyanide (K[Ag(CN) ₂ ]) and 90 g/L of potassium cyanide (KCN), the plate sample having the base nickel plating layer formed thereon was used as a cathode, and a titanium electrode plate coated with platinum was used as an anode. Electroplating was performed at a current density of 2.0 A/dm ² for 10 seconds at room temperature (25° C.) while stirring at 500 rpm using a stirrer to form a silver strike plating film. Then, the silver strike plating solution was fully rinsed by washing with water.

(Silver plating process)

In a silver plating solution containing 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 sodium 2-mercaptobenzothiazole (C ₇ H ₄ NNaS ₂ ) as a substance belonging to benzothiazoles or derivatives thereof, the plate sample formed with the silver strike film as a cathode and the silver electrode plate as an anode were electroplated for 18 seconds under the conditions of a liquid temperature of 35° C. and a current density of 7 A/dm ² while stirring at 500 rpm with a stirrer to form a silver coating layer. The concentration of free cyanide in the silver plating solution was 38 g/L. The thickness of the silver coating layer was measured at the center of the surface of the plate sample using the above-mentioned fluorescent X-ray film thickness meter and the result was about 1 μm. In this way, a silver-plated material having silver coating layers on both sides of the plate was obtained.

The obtained silver-plated material was used as a test material and subjected to the following test.

(Constant temperature and humidity test)

The test material was placed in a constant temperature and humidity test apparatus (manufactured by Isuzu Corporation, TPAV-48-20) and maintained at a temperature of 85°C and a relative humidity of 85%. The holding time was set at two levels: 120 hours and 144 hours.

(Bending test)

After the plate subjected to the above-mentioned constant temperature and humidity test was bent by hand by 180°, the bent portion was folded back to the roughly original plate shape, and the outer and inner surfaces of the bent portion were observed to check whether the silver coating layer peeled off. In the bending test, the case where no peeling (falling off) or floating of the silver coating layer was found on both the outer and inner surfaces of the bent portion was recorded as ◎ (stripping resistance: excellent), the case where no peeling (falling off) of the silver coating layer was found on both the outer and inner surfaces of the bent portion, but slight floating was found on at least one of the silver coating layers was recorded as ○ (stripping resistance: good), and the case where the silver coating layer peeled off (falling off) was found on at least one of the outer and inner surfaces of the bent portion was recorded as × (stripping resistance: poor), and the evaluation of ○ or above was judged as qualified. The holding time of the test material obtained in this example at the two levels of the constant temperature and humidity test was all evaluated as ×.

(Peel test using cross-cut peeling)

For the plate subjected to the above-mentioned constant temperature and humidity test, a straight cut deeper than the thickness of the silver coating layer is formed on the surface (plated surface) of the silver coating layer on both sides at intervals of 3 mm using a cutter in two orthogonal directions, thereby forming more than 100 3 mm square grids, and a peeling test is performed using the method of the peeling test method using an adhesive tape specified in Item 15.1 of JIS H8504:1999. For all the grids, a peeling test using an adhesive tape is performed, and the peeling area ratio (%) expressed by 100×[number of grids where peeling occurred]/[total number of grids] is calculated. The case where the peeling area ratio is 0% (no peeling) is recorded as ◎, the case where the peeling area ratio exceeds 0% and is less than 3% is recorded as ○, the case where the peeling area ratio exceeds 3% is recorded as ×, and the evaluation of ○ or above is judged as qualified. In this test, the sample that was evaluated as ○ in the material kept at the constant temperature and humidity test for 120 hours can be evaluated as having excellent peeling resistance equal to or better than that of conventional general silver-plated materials. The test material obtained in this example was evaluated as × in both the holding time levels of the constant temperature and humidity test.

(Reciprocating sliding test)

Two silver-plated materials were prepared as test materials. One of them was indented (R = 1.5 mm on the inside) and used as an indenter. The other was used as a flat evaluation sample. A precision sliding test device (CRS-G2050-DWA manufactured by Yamazaki Seiki Laboratory Co., Ltd.) was used to push the indenter against the evaluation sample with a certain load (5N) while performing a reciprocating sliding action (sliding distance 5mm, sliding speed 1.67mm/s). For the evaluation sample that was subjected to the reciprocating sliding test until the specified number of times, a microscope (VHX-1000 manufactured by KEYENCE Co., Ltd.) was used to observe the sliding marks at a magnification of 100 times to examine the wear state of the silver coating layer. In a material having a silver coating layer with a film thickness of about 1 μm, if the copper of the substrate is not exposed in the sliding marks at the stage where the number of reciprocating sliding according to the test conditions is 100 times, it can be judged that the silver coating layer has excellent wear resistance. Therefore, when the number of reciprocating slides reached 100 times, the copper of the base material was exposed in the sliding marks, which was rated as × (wear resistance: insufficient), and otherwise as ○ (wear resistance: good). In the case of the test material of this example, the copper of the base material was not exposed at the 400th sliding number, and the sliding test was terminated at this stage. Since the copper was not exposed even at the 400th sliding number, the wear resistance was rated as ○. In this case, the number of sliding times at which the copper of the base material was exposed is indicated as "more than 400" in Table 2.

The production conditions of the test materials are summarized in Table 1, and the results of the investigation are summarized in Table 2 (the same applies to the following examples).

[Example 1]

The silver-plated material obtained by the silver-plating process under the same conditions as those in Comparative Example 1 was subjected to the heat treatment process described below.

(Heat treatment process)

Here, for the purpose of the experiment, the silver coating layer of the plate sample (silver-plated material) obtained in the above-mentioned silver plating process was heat-treated using the temperature control function of the table-top hot stirrer. Specifically, the temperature of the table-top hot stirrer was set to 180°C. After the temperature stabilized at the set value, the plate sample was placed on the flat plate surface of the table-top hot stirrer so that the silver coating layer on one side of the plate sample was in close contact with the plate surface of the table-top hot stirrer. After 5 seconds from the start of placement, the plate sample was removed from the plate surface of the table-top hot stirrer and cooled in the air at room temperature. That is, the placement time was 5 seconds. In this experiment, heating was performed from one side of the surface, but by measuring the heating curve of the preliminary experiment, it was confirmed that the surface on the opposite side of the plate surface of the table-top hot stirrer also rapidly increased in temperature, and the maximum reaching temperature T _MAX of the silver coating layers on both sides was approximately equal to the set temperature of the table-top hot stirrer, and the time for the silver coating layers on both sides to be maintained in the temperature range of 150°C or more and T _MAX (°C) or less was approximately the same as the placement time. Therefore, in this example, the time for which the silver coating layers on both sides are maintained in the temperature range of 150° C. or higher and 180° C. or lower (T _MAX ) is considered to be 5 seconds.

The plated material that had completed the heat treatment process was used as a test material, and the same test as in Comparative Example 1 was performed. As a result, at the two levels of holding time in the constant temperature and humidity test, the bending test was evaluated as ◎, the peeling test using cross-cut peeling was evaluated as ◎, and the reciprocating sliding test was evaluated as ○. That is, the silver coating layer after the above heat treatment can have both excellent wear resistance and peeling resistance.

[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 step. As a result, the bending test was evaluated as ◎ at the two levels of holding time in the constant temperature and humidity test, the peeling test using cross-cut peeling was evaluated as ◎, and the reciprocating sliding test was evaluated as ○. That is, the silver coating layer after the heat treatment can have both excellent wear resistance and peeling resistance.

[Example 3]

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 and the placement time on the tabletop hot stirrer was set to 10 seconds during the heat treatment process. As a result, the bending test was evaluated as ◎ at the two levels of holding time in the constant temperature and humidity test, the peeling test using cross-cut peeling was evaluated as ◎, and the reciprocating sliding test was evaluated as ○. That is, the silver coating layer after the heat treatment can have both excellent wear resistance and peeling resistance.

[Example 4]

The experiment was conducted in the same manner as in Example 1, except that the temperature of the tabletop hot stirrer was set to 250°C and the constant temperature and humidity test was conducted at only one level with a holding time of 120 hours in the heat treatment process. As a result, for the material held in the constant temperature and humidity test for 120 hours, the bending test was evaluated as ◎, the peeling test using cross-cut peeling was evaluated as ◎, and the reciprocating sliding test was evaluated as ○. That is, the silver coating layer after the heat treatment can have both excellent wear resistance and peeling resistance.

[Example 5]

The experiment was conducted in the same manner as in Example 1 except that the temperature of the tabletop hot stirrer was set to 160°C and the placement time on the tabletop hot stirrer was set to 20 seconds during the heat treatment process. As a result, the bending test was evaluated as ◎ at the two levels of holding time in the constant temperature and humidity test, the peeling test using cross-cut peeling was evaluated as ◎, and the reciprocating sliding test was evaluated as ○. That is, the silver coating layer after the heat treatment can have both excellent wear resistance and peeling resistance.

[Example 6]

The experiment was conducted in the same manner as in Example 1, except that the concentration of sodium 2-mercaptobenzothiazole (C ₇ H ₄ NNaS ₂ ) in the silver plating solution was 25 g/L (=0.13 mol/L) in the silver plating step, the temperature of the table-top hot stirrer was set at 200°C in the heat treatment step, and the constant temperature and humidity test was conducted only at one level of holding time of 120 hours. As a result, for the material held in the constant temperature and humidity test for 120 hours, the bending test was evaluated as ◎, the peeling test using cross-cut peeling was evaluated as ◎, and the reciprocating sliding test was evaluated as ○. That is, the silver coating layer after the heat treatment can have both excellent wear resistance and peeling resistance.

[Example 7]

The experiment was conducted in the same manner as in Example 1, except that the concentration of sodium 2-mercaptobenzothiazole (C ₇ H ₄ NNaS ₂ ) in the silver plating solution was 35 g/L (=0.18 mol/L) in the silver plating step, the temperature of the table-top hot stirrer was set at 200°C in the heat treatment step, and the constant temperature and humidity test was conducted only at one level of holding time of 120 hours. As a result, for the material held in the constant temperature and humidity test for 120 hours, the bending test was evaluated as ◎, the peeling test using cross-cut peeling was evaluated as ◎, and the reciprocating sliding test was evaluated as ○. That is, the silver coating layer after the heat treatment can have both excellent wear resistance and peeling resistance.

[Example 8]

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 70 g/L in the silver plating process, the 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 with a holding time of 120 hours. It should be noted that the concentration of free cyanide in the silver plating solution was 28 g/L. As a result, for the material kept in the constant temperature and humidity test for 120 hours, the bending test was evaluated as ○, the peeling test using cross cutting peeling was evaluated as ○, and the reciprocating sliding test was evaluated as ○. That is, for the silver coating layer after the above heat treatment, it can have both excellent wear resistance and good peeling resistance.

[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 120 g/L in the silver plating process, the temperature of the table-top hot stirrer was set to 200°C in the heat treatment process, and the constant temperature and humidity test was performed only at one level with a holding time of 120 hours. It should be noted that the concentration of free cyanide in the silver plating solution was 48 g/L. As a result, for the material kept in the constant temperature and humidity test for 120 hours, the bending test was evaluated as ◎, the peeling test using cross cutting peeling was evaluated as ◎, and the reciprocating sliding test was evaluated as ○. That is, for the silver coating layer after the above heat treatment, it can have both excellent wear resistance and peeling resistance.

[Comparative Example 2]

The experiment was conducted in the same manner as in Comparative Example 1, except that in the silver plating step, a silver plating solution containing no benzothiazole or its derivatives and 37 g/L of selenium was used, the solution temperature was set to 18° C., and the power-on time was set to 90 seconds to perform electroplating silver. It should be noted that the concentration of free cyanide in the silver plating solution was 38 g/L. As a result, the thickness of the obtained silver coating layer was 5 μm, and the wear resistance was inferior to that of the silver coating layer of Comparative Example 1 formed using a silver plating solution containing benzothiazole or its derivatives.

[Comparative Example 3]

The experiment was conducted in the same manner as in Comparative Example 1, except that in the silver plating step, a silver plating solution containing no benzothiazole or its derivatives and 69 g/L of selenium was used, the solution temperature was 18°C, the current density was 5 A/dm ² , and the energization time was 120 seconds. The concentration of free cyanide in the silver plating solution was 38 g/L. As a result, the thickness of the obtained silver coating layer was 5 μm, and the wear resistance was inferior to that of the silver coating layer of Comparative Example 1 formed using a silver plating solution containing benzothiazole or its derivatives.

[Comparative Example 4]

The experiment was conducted in the same manner as in Example 1, except that the temperature of the tabletop hot stirrer was set to 350°C in the heat treatment process and the constant temperature and humidity test was performed at only one level with a holding time of 120 hours. As a result, for the material held in the constant temperature and humidity test for 120 hours, the bending test was evaluated as ◎, and the peeling test using cross-cut peeling was evaluated as ◎. However, the reciprocating sliding test was evaluated as ×. That is, if the heat treatment temperature is too high, the wear resistance improvement effect produced by using a silver plating solution containing benzothiazoles or derivatives thereof is impaired.

＜Elemental analysis of silver coating layer＞

The composition analysis of the silver coating layer was performed on the test materials obtained in Examples 2, 6, and 7 (all of which were heat-treated) and the test materials obtained in Comparative Examples 1 and 3 (all of which were not heat-treated) by the following method.

From the outermost surface of the silver coating layer of the test material, the element concentration distribution in the depth direction was measured by XPS (X-ray photoelectron spectroscopy) for each element of C, O, S, Ag, K, Ni, and N in Examples 2, 6, 7, and Comparative Example 1, and for each element of C, Se, S, and Ag in Comparative Example 3. It should be noted that Se was not detected in Examples 2, 6, 7, and Comparative Example 1 (less than 0.014 at% (less than 0.01 mass%)).

As an X-ray photoelectron spectrometer, PHI5000VersaProbeI II manufactured by ULVAC-PHI Co., Ltd. was used. For the measurement, the following settings were set: ultimate vacuum degree: 10 ^-7 Pa, excitation source: monochromatized AlKα, output: 25 W, acceleration voltage: 15 kV, beam size: 100 μmΦ, incident angle: 90 degrees, electron beam irradiation was performed using an electron neutralization gun at an emission current: 20 μA, bias voltage: 1.0 V, and acceleration voltage: 30.0 V, and argon ion irradiation was performed using an argon ion gun at an ion species: Ar ⁺ , acceleration voltage: 0.11 kV, and emission current: 7 mA, and the photoelectron extraction angle was set to 45 degrees, the number of accumulations: 5 times, the integration time: 40 ms (20 ms×2), the pass energy: 140 eV, and the measurement energy interval: 0.25 eV/step.

The surface etching for the analysis in the depth direction was carried out using an argon ion gun under the conditions of ion species: Ar ⁺ , acceleration voltage: 4 kV, emission current: 20 mA, scanning area: 2.7 mm × 2.7 mm, and sputtering rate: 20 nm/min (SiO ₂ conversion). As for the intervals for adjusting the etching time to each measured depth, in Examples 2, 6, and 7, the intervals were 1 minute until the cumulative etching time was 0 to 20 minutes, and thereafter the intervals were 0.25 minutes, in Comparative Example 1, the intervals were 2 minutes until the cumulative etching time was 0 to 20 minutes, and thereafter the intervals were 4 minutes, and in Comparative Example 3, the intervals were 0.1 minutes until the cumulative etching time was 0 to 3 minutes, and thereafter the intervals were 0.2 minutes.

As the spectral species for determining the atomic concentration, the peak of the binding energy of the 3d orbital (Ag3d) was used for Ag, the peak of the binding energy of the 1s orbital (C1s) was used for C, and the peak of the binding energy of the 2p orbital (S2p) was used for S. The Shirley method was used for background processing.

1 to 5 show the element concentration distribution in the depth direction of the silver coating layer of each test material by XPS. FIG. 1 is Example 2, FIG. 2 is Example 6, FIG. 3 is Example 7, FIG. 4 is Comparative Example 1, and FIG. 5 is Comparative Example 3.

In these element concentration distributions, as data in the internal area of the silver coating layer where there is no influence of contamination near the outermost surface and the influence of concentration changes near the interface with the base metal, in Examples 2, 6, 7 and Comparative Example 1, the values of the average Ag concentration, average C concentration, and average S concentration expressed in atomic % at the depth position corresponding to an etching time of 10 to 25 minutes were used, and in Comparative Example 3, the values of the average Ag concentration, average C concentration, and average S concentration expressed in atomic % at the depth position corresponding to an etching time of 5 to 15 minutes were used to calculate the values of average C concentration/average Ag and average S concentration/average Ag concentration, and these values were used as the C/Ag molar ratio and S/Ag molar ratio of the silver coating layer of each test material.

Table 2 shows the results.

[Table 1]

[Table 2]

Claims (9)

1. A method of manufacturing a silver plating material, comprising: an electroplated silver step of forming a silver coating layer on the blank by an electroplating method using a cyanide-containing silver plating solution in which benzothiazoles or derivatives thereof are dissolved; and

And a heat treatment step of maintaining the silver coating layer at a temperature range of 150 to 300 ℃ for 3 to 30 seconds.

2. The method for producing a silver plating material according to claim 1, wherein the silver plating solution is a solution in which benzothiazoles or derivatives thereof are dissolved at 0.01 to 0.80 mol/L.

3. The method for producing a silver plating material according to claim 1, wherein in the step of plating silver, a silver coating layer containing C, S and having 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.

4. The method for producing a silver plating material according to claim 1, wherein in the silver electroplating step, mercaptobenzothiazole or a derivative thereof is used as a substance belonging to the benzothiazole group or a derivative thereof.

5. A method of producing silver plating material according to claim 1, wherein the base material of the blank has copper or a copper alloy.

6. The method for producing a silver plating material according to claim 1, wherein the blank is formed with a silver strike plating film on a surface thereof.

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

8. A silver-coated metal sheet material comprising a metal sheet having a copper or copper alloy as a base material and, formed on the surface thereof, a silver coating layer containing C, S and having a C/Ag molar ratio of 0.030 to 0.200 and a S/Ag molar ratio of 0.005 to 0.050, wherein the silver coating layer exhibits peel resistance such that the peel area ratio of the silver coating layer is 3% or less when the silver-coated metal sheet material is subjected to a peel test under conditions of a temperature of 85 ℃ and a relative humidity of 85% for 120 hours,

(Peel test)

By forming linear cuts deeper than the thickness of the silver coating layer at 3mm intervals on the surface of the silver coating layer by using a cutter blade at two orthogonal directions, 100 or more square squares of 3mm are formed, and all square squares are formed by using a method according to JIS H8504:1999, 15.1, and the value expressed by 100× [ number of squares where peeling occurred ]/[ total number of squares ] is set as the peeling area ratio (%).

9. An energized part in which the silver-coated metal sheet material according to claim 8 is used for a material.