JP2013036072A - Coated composite material for moving contact part, moving contact part, switch, and method for production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silver-coated composite material for a moving contact part, in which the adhesion of a plating film is well resistant to repeated shear stress, the contact resistance remains low and stable over a long term, and the life of a switch is improved, and to provide a moving contact part.SOLUTION: In the silver-coated composite material for a moving contact part, an undercoat comprising any one of nickel, cobalt, a nickel alloy, and a cobalt alloy is formed on at least a part of the surface of a stainless steel substrate, an intermediate layer comprising copper or a copper alloy is formed thereon, and a silver or silver alloy layer as the outermost layer is formed thereon, wherein the thickness of the intermediate layer is 0.05-0.3 μm, and the average crystal grain diameter of the silver or the silver alloy formed as the outermost layer is 0.5-5.0 μm.

Description

  The present invention relates to an electrical contact component and a material thereof, and more particularly to a silver-coated composite material for a movable contact component and a movable contact component used for a movable contact in a small switch used in an electronic device or the like, and a manufacturing method thereof.

  A disc spring contact, a brush contact, and a clip contact are mainly used for electrical contact portions such as connectors, switches, and terminals. For these contact parts, a composite contact material in which a base material excellent in corrosion resistance and mechanical properties such as copper alloy and stainless steel is coated with silver excellent in electrical characteristics and solderability is frequently used.

  Of these composite contact materials, those using stainless steel as the base material are superior in mechanical properties and fatigue life to those using a copper alloy as the base material. It is used for movable contacts such as long-acting tactile push switches and detection switches. In recent years, it has been frequently used for push buttons of mobile phones. Due to the enhancement of mail functions and Internet functions, the number of switch operations has increased dramatically, and long-life movable contact parts are required.

  Compared to composite contact materials using copper alloy as the base material, the composite contact material using stainless steel as the base material can reduce the size of the movable contact parts, thereby miniaturizing the switch and increasing the number of operations. However, the contact pressure of the switch is increased, and there is a problem of wear of silver coated on the movable contact parts and a decrease in contact life due to a significant increase in the number of operations.

  For example, as a composite contact material in which a silver strip or a silver alloy is coated on a stainless steel strip, a material obtained by applying nickel plating to a base is frequently used (for example, see Patent Document 1). However, when this is used for a switch, as the number of switch operations increases, the silver at the contact part is scraped off due to wear, the underlying nickel plating layer is exposed, the contact resistance increases, and there is a problem that conduction cannot be achieved. It has become. In particular, this phenomenon is likely to occur in small-diameter dome-shaped movable contact parts, which is a major technical problem for switches that are becoming increasingly smaller.

  In order to solve this problem, there is a composite contact material in which a nickel plating layer and a palladium plating are sequentially applied on a base material, and then gold plating is applied thereon (see, for example, Patent Document 2). However, since the palladium plating film is hard, there is a problem that cracks are likely to occur when the number of switch operations increases.

  In addition, there is one in which nickel plating, copper plating, nickel plating, and gold plating are sequentially applied to a stainless steel base for the purpose of improving conductivity (see Patent Document 3). However, although nickel plating itself is excellent in corrosion resistance, since it is hard, cracks may occur in the nickel plating layer between the copper plating layer and the gold plating layer during bending, and as a result, the copper plating layer is exposed and corrosion resistance There is a problem of deterioration.

  In addition, as a technology for improving the contact life, there is a technique in which nickel plating, copper plating, and silver plating are sequentially applied to a stainless steel substrate (see Patent Documents 4 to 6). In these technologies, attempts were made to improve the contact life. As a result, the initial contact resistance value after heat treatment simulating soldering at the time of contact module formation (for example, at a temperature of 260 ° C. for 5 minutes) and the contact resistance value after performing a keystroke test for 1 million times were measured. Many products that cannot be used as products due to high contact resistance after heat treatment have appeared. This indicates that the defect rate when incorporated into a product increases, and simply forming a base nickel layer, an intermediate copper layer, and a silver outermost layer in a predetermined thickness on a stainless steel substrate in that order. It was found that the contact characteristics and contact life after heat history and keystroke were insufficient. In particular, in the process of module formation, soldering, and the like, oxidation of the base layer is generated by oxygen that has permeated silver, and then the peeling of the silver plating layer is induced by a key-pressing test that generates repeated strain.

  Further, as a technique for improving the contact life, in an electrical contact material in which the surface of a strip made of copper or a copper alloy is coated with a layer made of silver or a silver alloy, the crystal grain size of the silver or the silver alloy has an average An electrical contact material characterized by having a value of 5 μm or more is provided, and a silver or silver alloy plating layer is formed on the surface of the strip made of copper or copper alloy, and then in a non-oxidizing gas atmosphere , A method for producing an electrical contact material, characterized in that heat treatment is performed at a temperature of 400 ° C. or higher (Patent Document 7). However, if a composite contact material in which silver or a silver alloy is coated on a stainless steel strip is subjected to heat treatment at 400 ° C. or higher in order to control the crystal grain size of the silver or silver alloy to 5 μm or more, the spring characteristics of the stainless steel strip are It was found that the material was deteriorated and could not be applied as a movable contact material. Furthermore, nickel or a nickel alloy is used for the intermediate layer, and a configuration in which a copper component is present in the intermediate layer as an upper layer of the underlayer is not disclosed.

JP 59-219945 A Japanese Patent Laid-Open No. 11-232950 JP-A-63-137193 JP 2004-263274 A JP 2005-002400 A JP 2005-133169 A JP 05-002940 A

  As a composite material for movable contact parts, the present invention provides a silver for movable contact parts that has excellent plating adhesion even against repeated shear stress, a low and stable contact resistance value over a long period of time, and an improved switch life. An object is to provide a covering composite material, a movable contact part, and a switch.

  As a result of intensive studies in view of the above problems, the present inventors have formed a base layer made of nickel, cobalt, nickel alloy, or cobalt alloy on at least a part of the surface of the stainless steel substrate, and copper or copper on the upper layer. An average crystal of silver or silver alloy formed on the outermost layer in the silver-coated composite material for movable contact parts, in which an intermediate layer made of a copper alloy is formed and a silver or silver alloy layer is further formed on the upper layer. By controlling the particle size to 0.5 μm or more, it has excellent plating adhesion even against repeated shear stress, low contact resistance even after thermal history, and low and stable contact resistance over a long period of time I found out that I can. Further, the present inventors have found that the effect of controlling the crystal grain size is further enhanced by controlling the thickness of the copper or copper alloy formed in the intermediate layer in the range of 0.05 to 0.3 μm. It came.

The present invention provides the following solutions.
(1) A base layer made of nickel, cobalt, a nickel alloy, or a cobalt alloy is formed on at least a part of the surface of the stainless steel substrate, and an intermediate layer made of copper or a copper alloy is formed thereon, and A silver-coated composite material for a movable contact part in which a silver or silver alloy layer is formed as an outermost layer on an intermediate layer, wherein the intermediate layer has a thickness of 0.05 to 0.3 μm, and A silver-coated composite material for movable contact parts, wherein an average crystal grain size of silver or a silver alloy formed on a surface layer is 0.5 μm or more.
(2) The silver-coated composite material for movable contact parts according to (1), wherein the thickness of the outermost layer is 0.3 to 2.0 μm.
(3) A movable contact part formed by processing the silver-coated composite material for a movable contact part according to (1) or (2), wherein the contact part is formed in a dome shape or a convex shape. Movable contact parts.
(4) A switch using the movable contact component according to (3), wherein the movable contact component and a fixed contact connected to the movable contact component are incorporated in a resin case. switch.
(5) forming an underlayer made of nickel, cobalt, nickel alloy or cobalt alloy on at least a part of the surface of the stainless steel substrate, and forming an intermediate layer made of copper or copper alloy on the upper layer; A method for producing a silver-coated composite material for a movable contact part, in which a silver or silver alloy layer is formed as an outermost layer on an intermediate layer, wherein the silver and silver alloy plating forming the outermost layer allows its cathode current density. A method for producing a silver-coated composite material for movable contact parts, wherein the method is performed at 80% or more of the current density.
(6) The method for producing a silver-coated composite material for a movable contact part according to (5), wherein the heating is performed after the silver and silver alloy plating.
(7) The current-carrying heating is carried out between a silver and silver alloy plating electrolytic cell and a power supply device disposed on the outlet side of the electrolytic cell. The silver-coated composite for movable contact parts according to (6) A method of manufacturing the material.
(8) The method for producing a silver-coated composite material for a movable contact part according to (6) or (7), wherein the energization heating is performed with a current of 4 A or more per 1 mm ² of a cross-sectional area of the strip.

Compared with the conventional movable contact material, the silver-coated composite material for movable contact parts of the present invention does not reduce the adhesion of the silver coating layer against repeated shear stress. In addition, a silver-coated composite material for movable contact parts that further improves the life of the switch is provided by keeping the contact resistance value low and stable over a long period of time, even during switch formation and when the switch is opened and closed. it can.
Moreover, the movable contact part of this invention processes the said silver covering composite material for movable contact parts, and generation | occurrence | production of the crack of each layer after processing into a dome shape or convex shape is suppressed. Therefore, the contact resistance value is kept low and stable over a long period of time, and the movable contact part has a long contact life. In particular, the effect is large in a dome-shaped contact where a repeated shear stress is applied.

It is the block diagram which showed a preferable example of schematic structure of a plating apparatus. It is a top view of the switch used for the keystroke test. The AA sectional view and pressing direction in the top view of the switch used for the keystroke test are shown, (a) before the switch operation, (b) at the time of the switch operation. It is the photograph which observed the silver coating composite material for movable contact parts of this invention by EBSD, and shows the example whose average crystal grain diameter is about 0.6 micrometer. It is the photograph which observed the conventional silver covering composite material for movable contact parts by EBSD, and shows the example whose average crystal grain size is about 0.2 micrometer.

  Preferred embodiments of the silver-coated composite material for movable contact parts and the movable contact parts of the present invention will be described in detail.

  In the basic embodiment of the present invention, nickel, cobalt, nickel alloy or cobalt alloy underlayer, copper or copper alloy intermediate layer, crystal grain size is controlled on at least a part of the surface of the stainless steel substrate. A silver-coated composite material for movable contact parts in which the outermost layer of silver or silver alloy is formed in this order. The movable contact parts formed from this are unlikely to increase in contact resistance even if the number of switch operations increases. Is.

  In an embodiment of the present invention, the stainless steel substrate bears its mechanical strength when used in a movable contact part. For this reason, a rolled tempered material such as SUS301, SUS304, or SUS316, or a tension annealing material, which is a material that is excellent in stress relaxation properties and is not easily damaged by fatigue, is used as the stainless steel substrate.

  The underlayer formed on the stainless steel substrate is disposed in order to improve the adhesion between the stainless steel and the copper or copper alloy layer. The intermediate layer of copper or copper alloy can enhance the adhesion between the underlayer and the outermost layer, captures oxygen diffused in the outermost surface, prevents the oxidation of the components of the underlayer and improves the adhesion This is a known technique having a function.

  As the metal forming the underlayer, any of nickel, cobalt, nickel alloy, and cobalt alloy is selected as is well known, and nickel or cobalt is particularly preferable. This underlayer is formed by using a stainless steel substrate as a cathode and performing electrolysis using, for example, an electrolytic solution containing nickel chloride and free hydrochloric acid, or by subsequently forming two layers in combination with a nickel sulfamate bath or the like. The thickness is preferably 0.005 to 2.0 [mu] m in order to prevent cracking in the underlayer during press working, and more preferably 0.01 to 0.2 [mu] m.

  The cause of the conventional lowering of the adhesion of the outermost layer is due to the oxidation of the underlayer and the large repeated shear stress. As a countermeasure, the underlayer is not oxidized and the adhesion does not deteriorate even if shear stress is applied. It was necessary to develop a material that satisfies these two points.

Therefore, the present invention is based on a configuration in which an intermediate layer made of copper or a copper alloy is disposed as a means for preventing the base layer from being oxidized in order to solve the above-mentioned problems. The oxidation of the underlayer is due to the permeation of oxygen in the outermost layer. Depending on the arrangement of copper or copper alloy, the copper component diffused through the silver grain boundaries captures oxygen in the outermost layer and suppresses the oxidation of the underlayer. By doing so, it is considered to play a role of preventing a decrease in adhesion.
However, when this component is used as a silver-coated stainless steel part for movable contacts, there has been a problem that the contact resistance value increases. When the present inventors investigated this problem, the copper component of the intermediate layer easily diffused into the silver forming the outermost layer, and the diffused copper component reached the surface of the outermost layer. It has been clarified that this phenomenon is sometimes caused by oxidation to form copper oxide and increase contact resistance.

  As a result of diligent research to solve this phenomenon, it was found that the diffusion of copper, which is an intermediate layer component, to the outermost layer is closely related to the crystal grain size of silver forming the outermost layer. That is, it has been found that by increasing the crystal grain size of silver forming the outermost layer, the copper diffusion path can be significantly reduced and the amount of copper diffusion can be reduced.

  By controlling the crystal grain size of the outermost layer made of silver or silver alloy in the present invention to 0.5 μm or more, the diffusion amount of the copper component formed in the intermediate layer can be suppressed. Even with excellent plating adhesion, the contact resistance does not increase even when heat history is applied, and the contact resistance value does not increase even when used for a long time as a movable contact part. Silver coated composites can be provided.

  If the crystal grain size is less than 0.5 μm, there are many diffusion paths for the copper component in the intermediate layer due to an increase in crystal grain boundaries, so there is a high possibility that the heat resistance will be insufficient and the contact resistance will increase. Thus, it is preferable that the crystal grain size is increased to 0.5 μm or more because the diffusion path of the copper component in the intermediate layer is reduced. Particularly preferably, the crystal grain size is 0.75 μm or more.

  The crystal grain size of the outermost layer made of silver and a silver alloy in the conventional composite contact material has an average crystal grain size of about 0.2 μm, and as a result, is a path through which the copper component and oxygen in the intermediate layer diffuse. It is thought that there were many crystal grain boundaries in the outermost layer, which was a major cause of lower adhesion between layers and contact resistance.

  As a method of adjusting the crystal grain size of silver or silver alloy forming the outermost layer, the plating current density of silver and silver alloy is adjusted to 80% or more of the allowable current density to give a large internal stress to the plating film. Then, the crystal grain size can be increased by recrystallization by subsequent heating. The crystal grain size can be adjusted by adjusting the current density, energization heating current and time.

In the embodiment of the present invention, the thickness of the intermediate layer formed under optimum conditions is in the range of 0.05 to 0.3 μm. If the thickness of the intermediate layer is too thin, it is insufficient to capture the oxygen component that has permeated through the outermost layer. Conversely, if the thickness is too thick, the absolute amount of the copper component increases. Alternatively, even if the crystal grain size of the silver alloy is increased, the permeation of the outermost layer of the copper component cannot be sufficiently suppressed. Therefore, the thickness of the intermediate layer needs to be 0.3 μm or less. If it is the said range, a characteristic is fully satisfied, However, A more effective range is 0.08-0.2 micrometer, A particularly effective range is 0.1-0.15 micrometer.
In addition, when an intermediate | middle layer is formed with a copper alloy, the copper alloy which contains 1-10 mass% in total of 1 type, or 2 or more types of elements chosen from tin, zinc, and nickel is preferable. Although the component to be alloyed with copper is not necessarily limited, copper is the main component that improves the trapping of oxygen permeated through the silver layer and the adhesion with the silver or silver alloy that forms the underlayer and the outermost surface. When other alloy elements are contained, the intermediate layer becomes hard and wear resistance is improved. If the total of these elements is less than 1% by mass, the effect is almost the same as when the intermediate layer is pure copper, and if it exceeds 10% by mass, the intermediate layer becomes too hard, and the pressability may deteriorate. It is not preferable because cracking occurs during use as a contact point and corrosion resistance is lowered.

  The thickness of the outermost layer made of silver or a silver alloy is 0.3 to 2.0 μm, more preferably 0.5 to 2.0 μm, and still more preferably 0.8 to 1.5 μm. Thereafter, the copper component hardly diffuses into the outermost layer, and the contact stability is excellent. If the thickness of the outermost layer is too thin, even if the crystal grain size of silver or silver alloy forming the outermost layer is controlled, the copper component diffused from the intermediate layer will easily reach the surface layer, increasing the contact resistance. On the contrary, if the thickness is too large, the effect is saturated, and at the same time, the amount of silver used is increased.

  Examples of silver or silver alloy suitably used as the outermost layer include silver, silver-tin alloy, silver-indium alloy, silver-rhodium alloy, silver-ruthenium alloy, silver-gold alloy, silver-palladium alloy, silver- Nickel alloy, silver-selenium alloy, silver-antimony alloy, silver-zinc alloy, silver-bismuth alloy, etc. are mentioned, especially silver, silver-tin alloy, silver-indium alloy, silver-rhodium alloy, silver-ruthenium alloy And a silver-gold alloy, a silver-palladium alloy, a silver-nickel alloy, a silver-selenium alloy, and a silver-antimony alloy.

  In the present invention, the underlayer, intermediate layer, and outermost layer are each formed by electroplating. Each of the layers may be formed on the entire surface of the stainless steel substrate, but it is preferable to form the layers only on the contact portions because it is economical and a product with reduced environmental load can be provided.

The optimum plating current density of silver and silver alloy varies depending on the composition of the plating solution, bath temperature, and stirring conditions, but it can be adjusted to a current density of 80% or more with respect to the allowable current density under the plating conditions. is necessary.
The allowable current density is a current density immediately before the plating is burned by gradually increasing the plating current density. For example, when 5 A / dm ² is the allowable current density, 80% or more It is necessary to perform plating at 4 A / dm ² or more.
If it is less than 80%, recrystallization is difficult because the internal stress of silver and silver alloy is small, and it is necessary to recrystallize at a high temperature using a dedicated annealing furnace. It is preferable to carry out under the condition of 85% to 98% with respect to the allowable current density, and it is more preferred to carry out under the condition of 90% to 98%.

Since the silver and silver alloy plating layer obtained above have extremely large internal stress, the silver and silver alloy plating layer can be recrystallized by slight heating. As shown in FIG. 1, when the entire plating current is supplied only by the first rectifier 13 provided between the entrance side of the silver and silver alloy plating electrolytic cell 11 and the power supply device 12 on the cathode side, No heat is generated in the heating zone 14 on the outlet side 11. When the plating current is supplied by the second rectifier 16 between the power supply device 15 on the outlet side of the silver and alloy plating electrolytic cell 11 and the cathode side, the heating by using the electrical resistance of the stainless steel strip is effective. The amount of heat generated at this time also varies depending on the length of the heating zone 14, and the longer the length, the higher the electric resistance, so the amount of heat generated increases. Since the total current of the first and second rectifiers 13 and 16 becomes the plating current, the heat generation amount can be adjusted by the current distribution of the first and second rectifiers 13 and 16.
Therefore, since the stainless steel strip has a large specific resistance, it can be easily heated by energization, and the crystal grain size of the silver or silver alloy plating layer can be easily adjusted by the magnitude and time of the current. .
The energizing current of the second rectifier 16 is required to be 4 A or more per 1 mm ² of the cross-sectional area of the strip. When the current value is small, heat generation is insufficient and recrystallization does not occur. More preferably, it is 6 A or more, and particularly preferably 8 A or more. However, even if the current is too large, heat generation may be excessive and the material may be softened, so it is necessary to suppress it to 20 A or less at the maximum. .
Further, the length of the heating zone 14 on the outlet side of the electrolytic cell 11 is not limited, but it is desirable to set the length so that the heating time is about 2 to 30 seconds.

  In the following, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

  In a plating line in which a SUS substrate is continuously passed and wound, a substrate having a thickness of 0.05 mm and a width of 100 mm (SUS301 strip) is electrolytically degreased, washed with water, activated, washed with water, underlayer plating, washed with water, In the intermediate layer plating, water washing, silver strike plating, water washing, outermost layer plating, water washing, and drying processes, the current density of the outermost layer plating and the current value of the outermost layer plating outlet power supply device are changed, and the product of the present invention and the comparative product Got. Note that the passage time of the heating zone between the outermost layer plating and the outlet-side power feeding was 10 seconds.

  Each processing condition is as follows.

1. (Electrolytic degreasing, activation)
(Electrolytic degreasing)
Treatment liquid: sodium orthosilicate 100 g / liter Treatment temperature: 60 ° C
Cathode current density: 2.5 A / dm ²
Processing time: 10 seconds (activation)
Treatment liquid: 10% hydrochloric acid Treatment temperature: 30 ° C
Immersion treatment time: 10 seconds

2. (Underlayer plating)
(Nickel plating)
Treatment liquid: Nickel chloride 250 g / liter, Free hydrochloric acid 50 g / liter Treatment temperature: 40 ° C.
Current density: 5 A / dm ²
Plating thickness: 0.005 to 0.3 μm
Processing time: Adjust the time for each plating thickness (cobalt plating)
Treatment liquid: Cobalt chloride 250g / liter, Free hydrochloric acid 50g / liter Treatment temperature: 40 ° C
Current density: 2 A / dm ²
Plating thickness: 0.02-0.08 μm
Processing time: 2 seconds

3. (Interlayer plating)
(Copper plating 1: Indicated in the table as Cu-1)
Treatment liquid: copper sulfate 150 g / liter, free sulfuric acid 100 g / liter, free hydrochloric acid 50 g / liter Treatment temperature: 30 ° C.
Current density: 5 A / dm ²
Plating thickness: 0.05 to 0.32 μm
Processing time: Adjust the time for each plating thickness (Copper plating 2: Cu-2 in the table)
Treatment liquid: cuprous cyanide 30 g / liter, free cyanide 10 g / liter Treatment temperature: 40 ° C.
Current density: 5 A / dm ²
Plating thickness: 0.045 to 0.15 μm
Processing time: Adjust time for each plating thickness

4). (Silver strike plating)
Treatment liquid: silver cyanide 5 g / liter, potassium cyanide 50 g / liter Treatment temperature: 30 ° C.
Current density: 2 A / dm ²
Processing time: 10 seconds

5. (Outermost layer plating)
(Silver plating)
Treatment liquid: silver cyanide 50 g / liter, potassium cyanide 50 g / liter, potassium carbonate 30 g / liter Processing temperature: 40 ° C.
Current density: Changed in the range of 4.9 to 6.7 A / dm ² Plating thickness: 0.3 to 2.0 μm
Processing time: Adjust time for every plating thickness (silver-tin alloy plating) Ag-10% Sn
Treatment liquid: potassium cyanide 100 g / liter, sodium hydroxide 50 g / liter, silver cyanide 10 g / liter, potassium stannate 80 g / liter Treatment temperature: 40 ° C.
Current density: 6 A / dm ²
Plating thickness: 1.0 μm
Processing time: 0.3 minutes (silver-indium alloy plating) Ag-10% In
Treatment liquid: potassium cyanide (KCN) 100 g / liter, sodium hydroxide 50 g / liter, silver cyanide 100 g / liter, indium chloride 60 g / liter Processing temperature: 30 ° C.
Current density: 6 A / dm ²
Plating thickness: 1.0 μm
Processing time: 0.3 minutes The crystal grain size of silver and silver alloy of the obtained silver-coated stainless steel strip was obtained by taking an image with EBSD (electron beam backscatter diffraction) after section cutting with FIB, The crystal grain size was determined.

  The obtained silver-coated composite material (silver-coated stainless steel strip) for movable contact parts was processed into a dome-shaped movable contact part having a diameter of 4 mm, and the fixed contact was made of a brass strip plated with silver to a thickness of 1 μm. A keystroke test was conducted with the switch having the structure shown in FIGS. FIG. 2 is a plan view of the switch used for the key-stroke test. FIG. 3 is a cross-sectional view taken along line AA in FIG. 2 and the pressure of the switch used for the keystroke test. FIG. 3A is a diagram before the switch operation, and FIG. . As shown in FIGS. 2 and 3, a dome-shaped movable contact 1 made of silver-plated stainless steel and a fixed contact 2 made of silver-plated brass are incorporated in a resin case 4 with a resin filler 3.

In the keying test, a change in the contact resistance with time was measured by performing keying at a maximum of 1 million times at a contact stress of 9.8 N / mm ² and a keying speed of 5 Hz, and the results are shown in Tables 1 and 2. The contact resistance was measured with a current of 10 mA, and the contact resistance value including variations was evaluated in four stages. Specifically, a contact resistance value of less than 15 mΩ is evaluated as “excellent” and the table is marked with “◎”, and 15 mΩ or more and less than 30 mΩ is evaluated as “good”, and the table is marked with “◯”. A value of 30 mΩ or more and less than 50 mΩ was evaluated as “possible”, and a “Δ” mark was attached to the table, and a value of 50 mΩ or more was evaluated as “impossible” and an “x” mark was attached to the table. In addition, it was judged that the contact resistance value of less than 50 mΩ as a movable contact was ◎ to Δ having practicality as a contact.

Furthermore, whether the copper component was detected on the outermost surface was subjected to a qualitative analysis of the outermost surface with an Auger electron spectroscopy analyzer, and the detected amount of the copper component was investigated. Those that were not detected were shown as “None”, the detection amount of less than 5% as “trace amount”, and the detection amount as 5% or more as “large amount”.
In addition, the movable contact side after the keystroke test was visually inspected, and the presence or absence of peeling of the plating was observed to investigate the presence or absence of peeling.

  The silver-coated composite materials for movable contact parts of Invention Examples 1 to 20 are all increased in contact resistance by less than 30 mΩ even when subjected to a keystroke test of 1 million times after being processed as movable contact parts. In Comparative Examples 1 to 5, It can be seen that the contact resistance becomes 50 mΩ or more after 1 million times key pressing, and the contact life is short.

  Further, Comparative Example 1 is an example in which nickel plating is used as the conventional underlayer, copper plating is used as the intermediate layer, and silver plating is applied as the outermost layer. The silver crystal grain size of the outermost layer is about 0.2 μm. It can be seen that the contact resistance starts to increase after ten thousand times of keystrokes, and it becomes 50 mΩ or more at 50,000 times, which causes a practical problem. FIG. 4 shows a photograph of Invention Example 1 observed by EBSD (electron beam backscatter diffraction), and FIG. 5 shows a photograph of Comparative Example 1 observed by EBSD. The crystal grain size of silver in the outermost layer of Invention Example 1 in FIG. 4 is about 0.6 μm, and the crystal grain size of silver in the outermost layer of Comparative Example 1 in FIG. 5 is about 0.2 μm. Therefore, it can be seen that Invention Example 1 shows a good value of contact resistance as compared with Comparative Example 1. The crystal grain size was measured by dividing the cross-sectional area of the plating film of FIGS. 4 and 5 by the number of crystal grains and further obtaining the quotient as the square root.

Regarding Comparative Example 5, if the intermediate layer made of copper is in a thin state, peeling of the outermost layer / intermediate layer has occurred after 1 million keystrokes, and the trapping of permeated oxygen is insufficient, resulting in adhesion. I can hear that it is inferior.
As in Comparative Example 4, when the intermediate layer made of copper is thick, it can be seen that even if the crystal grain size is adjusted, diffusion of the copper component on the outermost surface is often observed, and as a result, the contact resistance value is increased. . On the other hand, in Comparative Examples 2 and 3 in which the crystal grain size is smaller than 0.5 μm, the diffusion amount of the copper component increases even if the intermediate layer thickness is controlled at 0.05 to 0.3 μm, and the surface of the outermost layer It can be seen that the exposure of the copper component increased and the contact resistance value increased.

  From these results, while controlling the thickness of the intermediate layer at 0.05 to 0.3 μm as in the inventive examples, the crystal grain size of the outermost layer made of silver or a silver alloy is in the range of 0.5 to 5.0 μm. It is clear that long-term reliability as a contact characteristic of movable contact parts can be improved by controlling to a stable, industrially stable silver-coated composite for movable contact parts that has excellent adhesion and long-term reliability. Can be provided.

DESCRIPTION OF SYMBOLS 1 Dome type movable contact 2 Moveable contact 3 Filler 4 Resin case

Claims (8)

A base layer made of nickel, cobalt, nickel alloy or cobalt alloy is formed on at least a part of the surface of the stainless steel substrate, an intermediate layer made of copper or copper alloy is formed on the upper layer, and silver is further formed on the upper layer. Or a silver-coated composite material for a movable contact part in which a silver alloy layer is formed as an outermost layer,
The movable layer characterized in that the thickness of the intermediate layer is 0.05 to 0.3 μm, and the average crystal grain size of silver or silver alloy formed on the outermost layer is 0.5 to 5.0 μm. Silver-coated composite material for contact parts.   2. The silver-coated composite material for a movable contact part according to claim 1, wherein a thickness of the outermost layer is 0.3 to 2.0 μm. A movable contact part formed by processing the silver-coated composite material for a movable contact part according to claim 1 or 2,
A movable contact part characterized in that the contact part is formed in a dome shape or a convex shape. A switch using the movable contact part according to claim 3,
A switch characterized in that the movable contact part and a fixed contact connected to the movable contact part are incorporated in a resin case. An underlayer made of nickel, cobalt, nickel alloy or cobalt alloy is formed on at least a part of the surface of the stainless steel substrate, an intermediate layer made of copper or copper alloy is formed on the upper layer, and silver is further formed on the upper layer. Or a method for producing a silver-coated composite material for a movable contact part, wherein a silver alloy layer is formed as an outermost layer,
The method for producing a silver-coated composite material for a movable contact part, wherein the silver and silver alloy plating forming the outermost layer is performed at a cathode current density of 80% or more of an allowable current density.   6. The method for producing a silver-coated composite material for a movable contact part according to claim 5, wherein an electric heating is performed after the silver and silver alloy plating.   The current-carrying heating is carried out between a silver and silver alloy plating electrolytic cell and a power feeding device arranged on the outlet side of the electrolytic cell. Production method. The method for producing a silver-coated composite material for a movable contact part according to claim 6 or 7, wherein the energization heating is performed at a current of 4 A or more per 1 mm ² in cross-sectional area of the strip.