JP5598851B2 - Silver-coated composite material for movable contact part, method for producing the same, and movable contact part - Google Patents

Description

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

  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.

  By the way, the composite contact material using stainless steel as the base material can reduce the size of the movable contact parts compared to the composite contact material using a copper alloy as the base material, so the switch can be downsized and the number of operations can be increased. However, the contact pressure of the switch is increased, and the contact life is reduced due to the wear of silver coated on the movable contact parts.

  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 operation of the switch increases, the silver of the contact part is scraped 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, nickel plating itself has excellent corrosion resistance but is hard, so 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). These techniques were tested for improved 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 after heat treatment simulating a keying test (for example, at a temperature of 200 ° C. for 1 hour) When the values were measured, many products that could not be used as products due to high contact resistance after heat treatment appeared. This indicates that the defect rate when incorporated in a product is increased, so simply forming a base nickel layer, an intermediate copper layer, and a silver outermost layer in a predetermined thickness on a stainless steel base material in that order. It is estimated that the contact characteristics and contact life after the heat history are insufficient.

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 by performing heat treatment at a temperature of 400 ° C. or higher has been proposed (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 shown.
Furthermore, in the method described in Patent Document 7, heat treatment is performed to adjust the crystal grain size, but the outermost surface is slightly oxidized due to the influence of residual oxygen in the inert atmosphere, increasing the contact resistance value. There is a possibility that. In addition, since a heat treatment step is required, there is a problem that the number of steps increases and the cost increases.

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-A-5-002940

  Therefore, the present invention is a composite material for movable contact parts, which has excellent plating adhesion even against repeated shear stress, has a low and stable contact resistance value over a long period of time, and does not undergo a heat treatment process. An object of the present invention is to provide a silver-coated composite material for a movable contact part and a movable contact part that can improve the service life of the contact point.

  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. A silver-coated composite material for a movable contact part, in which an intermediate layer made of a copper alloy is formed, and a silver or silver alloy layer is formed as an outermost layer on the intermediate layer, the silver or silver alloy formed on the outermost layer By controlling the internal stress within a specific range, the recrystallization is promoted by releasing the internal stress without passing through the heating step, thereby increasing the crystal grain size, resulting in a low contact resistance value. In addition, it has been found that the contact resistance can be kept low and stable over a long period of time. Furthermore, it has been found that the above effect 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. The present invention has been made based on these findings.

That is, the problem of the present invention is solved by the following means.
(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 component in which a silver or silver alloy layer is formed as an outermost layer on the upper layer, wherein the intermediate layer has a thickness of 0.05 to 0.3 μm, and the outermost layer A silver-coated composite material for movable contact parts, wherein the internal stress of the formed silver or silver alloy is 2.45 to 49.0 N / mm ² .
(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. A feature of movable contact parts.

The silver-coated composite material for movable contact parts of the present invention is excellent in terms of preventing a decrease in adhesion of the silver coating layer against repeated shear stress. Also, a silver-coated composite material for movable contact parts is provided that further improves the life of the switch by maintaining a low and stable contact resistance value over a long period of time, even during switch formation and when opening and closing the switch. it can.
Moreover, the movable contact part of this invention is processed using 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, it is possible to produce a movable contact part that has a low contact resistance value and is stable over a long period of time and has a long contact life.

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 a cross-sectional photograph in the silver covering composite material for movable contact parts of this invention, and shows the example whose average crystal grain diameter is about 0.75 micrometer. It is a cross-sectional photograph in the conventional silver coating composite material for movable contact parts, and shows an example in which the average crystal grain size is about 0.2 μm.

  A preferred embodiment of the silver-coated composite material for a movable contact part and the movable contact part of the present invention will be described in detail.

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

  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 annealed material, which is excellent in stress relaxation properties and is not easily damaged by fatigue, is preferably used as the stainless steel substrate.

  The underlayer formed on the stainless steel substrate has the effect of increasing the adhesion between the stainless steel and the copper or copper alloy layer. The intermediate layer of copper or copper alloy can improve the adhesion between the underlayer and the outermost layer, capture oxygen diffused in the outermost layer, prevent the oxidation of the components of the underlayer and improve the adhesion Has a function to maintain or maintain.

  The metal forming the underlayer is selected from nickel, cobalt, nickel alloy, and cobalt alloy, and nickel or cobalt is particularly preferable. The thickness of the underlayer is 0.005 to 2.0 μm by electrolysis using, for example, an electrolytic solution containing nickel chloride and free hydrochloric acid using a stainless steel base as a cathode. It is preferable for preventing cracks from forming in the formation, and is more preferably 0.01 to 0.2 μm.

  The cause of the decrease in the adhesion strength of the conventional outermost layer is due to the oxidation of the underlayer and a large amount of repeated shear stress. As countermeasures, 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, in the present invention, a configuration in which an intermediate layer made of copper or a copper alloy is arranged as a means for preventing the base layer from being oxidized. The oxidation of the underlayer is due to the permeation of oxygen in the outermost layer. Depending on the arrangement of the copper or copper alloy layer, the copper component diffused from the lower layer to the silver grain boundary captures oxygen in the outermost layer and the underlayer By suppressing the oxidation of the resin, it plays 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. As a result of investigations on this problem, the inventors of the present invention easily diffused the copper component of the intermediate layer into the silver forming the outermost layer, and the diffused copper component reached the surface of the outermost layer. It has been clarified that a phenomenon occurs that copper oxide is oxidized to increase contact resistance as an adverse effect.

  As a result of further earnest research to solve this phenomenon, the diffusion of copper, the intermediate layer component, to the outermost layer is closely related to the thickness of the intermediate layer and the crystal grain size of silver forming the outermost layer. I found. That is, when the intermediate layer is thin, the amount of copper diffusion is small even if the crystal grain size of silver forming the outermost layer is somewhat small, and when the intermediate layer is thick, the crystal grain size of silver forming the outermost layer is small. It has been found that the amount of copper diffusion can be reduced by increasing.

However, conventionally, many techniques for increasing the grain size by adding a thermal history have been disclosed as techniques for increasing the crystal grain size. However, the copper component of the intermediate layer is highly likely to diffuse into the surface layer due to its thermal history, and the copper component diffuses to the surface before the crystal grain size is coarsened, which oxidizes and increases the contact resistance. The cause was presumed to be the result. Therefore, as a result of earnest research, the present inventor, when forming silver or a silver alloy formed on the outermost layer by an electroplating method, the internal stress introduced at that time is 2.45 to 49.0 N / mm ² . As a result of the adjustment, the present inventors found that silver or a silver alloy can promote recrystallization using an internal stress as a driving force without going through a heating step, and can increase the crystal grain size.

By adjusting the internal stress of the outermost layer made of silver or silver alloy in the present invention to be 2.45 to 49.0 N / mm ² , the crystal grain size of silver or silver alloy is about 0. It is controlled in the range of 5 to 5.0 μm, can suppress the diffusion amount of the copper component formed in the intermediate layer, has excellent contact characteristics, especially does not increase the contact resistance even when a thermal history is applied, movable contact Since the contact resistance value does not increase even when used as a part for a long period of time, a silver-coated composite material for a movable contact part having good contact characteristics can be provided. In particular, since a heat treatment step is not required when adjusting the crystal grain size of silver or silver alloy, it is possible to provide a silver-coated composite material for movable contact parts that has a low and low contact resistance without promoting oxidation on the outermost surface. .
In the present invention, when the crystal grain size is shown, it means the average crystal grain size unless otherwise specified, and is measured using a cutting method according to JIS H0501, for example.

When the internal stress of the outermost layer is less than 2.45 N / mm ² , recrystallization due to the internal stress is hardly promoted and the crystal grain size becomes less than 0.5 μm. As a result, the number of crystal grain boundaries increases, so that there are many diffusion paths for the copper component in the intermediate layer, and the heat resistance becomes insufficient and the possibility that the contact resistance increases is increased. On the other hand, when the internal stress exceeds 49.0 N / mm ² , there is a high possibility that cracks develop on the outermost surface due to the high internal stress of the plating film itself. If cracks occur, not only will copper be promoted in the intermediate layer, but corrosion will likely occur due to the potential difference between the silver or silver alloy and the copper component, resulting in a sharp decrease in corrosion resistance. It is not preferable. If it is in the range of the above internal stress, it is preferably used, but if it is 4.9 to 29.4 N / mm ^2, it is excellent in long-term reliability and productivity, and cracking at the time of pressing is suppressed, so that it is more preferable. .

  The crystal grain size of the outermost layer made of silver and silver alloy in the conventional composite contact material is considered to be plated under the condition that the average crystal grain size is about 0.2 μm and there is almost no internal stress. It is done. As a result, there are many crystal grain boundaries in the outermost layer, which is a route through which the copper component and oxygen in the intermediate layer are diffused, and this is considered to be a major cause of a decrease in adhesion between layers and a deterioration in contact resistance.

In addition, it is preferable to form by the electroplating method as a method of adjusting the internal stress of the silver or silver alloy which forms the outermost layer. This method can be achieved by adjusting the additives and surfactants contained in the plating solution, various chemical concentrations, current density, plating bath temperature, stirring conditions, etc. 3 to 20 A / dm ² . Furthermore, in order to suitably introduce internal stress within this current density range, it is easily achieved by including 50 to 100 g / liter of Ag concentration as the plating solution composition and 25 to 50 g / liter of free cyanide concentration. Is done.
For example, increasing the internal stress can be achieved by increasing the electroplating current density and decreasing the silver concentration.
As a method for measuring internal stress, when verifying internal stress under plating conditions, for example, a glass bulb method, a contract meter method, a strain gauge method, and the like are known. For example, a spiral contract meter (( It can be measured by using Yamamoto Tekin Tester Co., Ltd., JIS H8626 compliant). In addition, as a method for measuring the internal stress of the formed plated product, it is known that it can be obtained by moving a diffraction peak or measuring a half value width by an X-ray measurement method.
In the present invention, using a spiral contractometer (manufactured by Yamamoto Sekin Tester Co., Ltd., JIS H8626 compliant), the spiral contractometer when a predetermined plating solution, current density and plating thickness are obtained by a JIS measurement method. The internal stress was measured by reading the angle and calculating it using a calculation formula.

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 less than 0.05 μm, it is insufficient to capture the oxygen component that has permeated through the outermost layer, and conversely if formed to exceed 0.3 μm, the absolute amount of the copper component Therefore, even if the crystal grain size of the silver or silver alloy forming the outermost layer is increased, the permeation of the outermost layer of the copper component cannot be sufficiently suppressed, so the thickness of the intermediate layer is 0.3 μm or less. There is a need. If it is the said range, a characteristic is fully satisfied, but a more 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 hardness of the intermediate layer is increased and the 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 hardness of the intermediate layer becomes too large, and the pressability is increased. It is not preferable because it deteriorates or cracks occur during use as a contact point and the corrosion resistance decreases.

  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. Even after being processed into contact parts, the copper component hardly diffuses into the outermost layer, and the contact stability is excellent. When the thickness of the outermost layer is less than 0.3 μm, even if the internal stress of silver or a silver alloy forming the outermost layer is controlled, the copper component diffused from the intermediate layer easily reaches the surface layer, so that the contact resistance On the other hand, if it exceeds 2.0 μm, the effect is saturated, and at the same time the amount of silver used is increased, which is not preferable in terms of economic and environmental load.

  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-copper alloy, silver-zinc alloy, silver-bismuth alloy, etc. are mentioned, especially silver, silver-tin alloy, silver-indium alloy, silver-rhodium alloy It is preferably selected from the group consisting of silver-ruthenium alloy, silver-gold alloy, silver-palladium alloy, silver-nickel alloy, silver-selenium alloy, silver-antimony alloy and silver-copper alloy.

  In the present invention, the underlayer, intermediate layer, and outermost layer can be formed by any method such as electroplating, electroless plating, physical / chemical vapor deposition, etc. From the most advantageous. In particular, the outermost layer made of silver or a silver alloy is preferably treated by the current density or the liquid composition in the electroplating method. The respective 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.

  In addition, in the silver or silver alloy into which internal stress is introduced according to the present invention, it is not necessary to perform heat treatment or the like, and the crystal grain size becomes coarse with time, but heat treatment is performed as necessary. It is also possible to rapidly increase the crystal grain size. In this case, since the driving force for recrystallization is sufficiently inherent due to internal stress, the heat treatment temperature may be processed at a low temperature of, for example, 40 to 100 ° C. It becomes possible to coarsen only.

  Hereinafter, 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 base material is continuously passed and wound up, a 0.06 mm thick and 100 mm wide base material (SUS301 strip) is electrolytically degreased, washed with water, activated, washed with water, underlayer plating, washed with water, Silver-coated stainless steel strips of Invention Examples 1 to 30 and Comparative Examples 1 to 3 having the configurations shown in Table 1 were obtained through the steps of intermediate layer plating, water washing, silver strike plating, outermost layer plating, water washing and drying.

  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: 0.01 to 0.2 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: 0.01 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 0.3 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 0.32 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: 93 g / liter of silver cyanide, 130 g / liter of potassium cyanide, 30 g / liter of potassium carbonate This composition corresponds to a silver content of 75 g / liter and a free cyanide concentration of 34 g / liter.
Processing temperature: 40 ° C
Current density: Adjusting internal stress by changing in the range of 1.0-18 A / dm ² (described in Table 1)
Plating thickness: 0.5 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, additive (here, sodium thiosulfate 0.5 g / liter)
Processing temperature: 40 ° C
Current density: 6 A / dm ²
Plating thickness: 2.0 μm
Processing time: 32 seconds (silver-indium alloy plating) Ag-10% In
Treatment liquid: potassium cyanide KCN 100 g / liter, sodium hydroxide 50 g / liter, silver cyanide 10 g / liter, indium chloride 20 g / liter, additive (here, sodium thiosulfate 0.5 g / liter)
Processing temperature: 30 ° C
Current density: 6 A / dm ²
Plating thickness: 2.0 μm
Processing time: 32 seconds

  Regarding the internal stress, the internal stress at each current density was measured in advance in the spiral stress measurement method, and the numerical values are shown in Table 1. In addition, the initial crystal grain size of each sample was approximately 0.2 μm.

  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 mmφ, and a brass strip plated with silver to a thickness of 1 μm was used for the fixed contact. A keystroke test was conducted with the switch having the structure shown in FIGS. FIG. 1 is a plan view of a switch used in the key-pressing test. 2A and 2B are cross-sectional views of the switch used in the keystroke test and FIG. 1A-A, and FIG. 2A shows a state before the switch operation, and FIG. In the figure, 1 is a silver-plated stainless steel dome-shaped movable contact, 2 is a silver-plated brass fixed contact, and these are incorporated in a resin case 4 with a resin filler 3.

In the keying test, contact resistance: 9.8 N / mm ² , keying speed: 5 Hz, a maximum of 1,000,000 times of keying was performed, and the change in contact resistance with time was measured. The results are shown in Table 1. 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 “◎”, 15 mΩ or more and less than 30 mΩ is evaluated as “good”, and the table is marked with “O”. 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 a contact point has practicality as a contact point when the contact resistance value is less than 50 mΩ and the evaluation is “good” or better (◎ to Δ).

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”.
Further, the movable contact side after the keystroke test was visually observed, and the presence or absence of peeling of the plating was observed to investigate the presence or absence of peeling.

In the silver-coated composite materials for movable contact parts of Invention Examples 1 to 30, the increase in contact resistance is less than 50 mΩ even when a keystroke test is performed 1 million times after processing as a movable contact part. 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 applied as the conventional underlayer, copper plating is applied as the intermediate layer, and silver plating is applied as the outermost layer, and the outermost layer silver has no internal stress. In this comparative example, it can be seen that the contact resistance starts to increase after 10,000 keystrokes and is 50 mΩ or more at 100,000 times, which causes a practical problem. FIG. 3 shows a photograph of the non-contact part of Invention Example 4 after the keystroke test observed with EBSD, and FIG. 4 shows a photograph of the non-contact part of Comparative Example 1 after the keystroke test observed with EBSD.
In FIG. 3, the lowermost black portion is a stainless steel portion, and the gray striped layer thereon is a silver plating layer. The nickel plating base layer and the copper plating intermediate layer are present between the stainless steel portion and the silver plating layer, but in the photograph, they are observed as black portions as with the stainless steel portion. The black part of the lowermost layer in FIG. 4 is a stainless steel part, and the cloud-like white layer thereon is a silver plating layer. The nickel plating base layer and the copper plating intermediate layer are present between the stainless steel portion and the silver plating layer, but in the photograph, they are observed as black portions as with the stainless steel portion.
As is apparent from the figure, the crystal grain size of the outermost silver having the internal stress in FIG. 3 (alternate gray portions in FIG. 3) is about 0.75 μm and is used as a movable contact part. In contrast, while the crystal grains are coarsened, in Comparative Example 1 in FIG. 4, the crystal grain size (the scattered white portion in FIG. 4) remains as small as about 0.2 μm. Thus, it can be seen that the contact resistance of the example of the present invention shows a good value as compared with Comparative Example 1, and has an internal stress of 2.45 to 49.0 N / mm ² during plating. It can be seen that this is effective in increasing the crystal grain size.

Regarding Comparative Example 2, 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 permeation of permeated oxygen is insufficient, resulting in adhesion. I can hear that it is inferior.
When the intermediate layer made of copper is thick as in Comparative Example 3, it can be seen that even if the internal stress is adjusted, a large amount of copper component is diffused on the outermost surface, and as a result, the contact resistance value is increased.

From these results, the internal stress of the outermost layer made of silver or a silver alloy was 2.45 to 49.0 N / mm ² while controlling the thickness of the intermediate layer at 0.05 to 0.3 μm as in the inventive examples. It is obvious that the long-term reliability as the contact characteristic of the movable contact part can be improved by controlling within the range.

1 Dome-shaped movable contact 2 Fixed contact 3 Filler 4 Resin case

Claims (3)

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, and an intermediate layer made of copper or copper alloy is formed on the upper layer, and further on the upper layer. A silver-coated composite material for a movable contact part in which a silver or silver alloy layer is formed as an outermost layer,
The thickness of the intermediate layer is 0.05 to 0.3 μm, and the internal stress of silver or the silver alloy formed on the outermost layer is 2.45 to 49.0 N / mm ^2. A silver-coated composite material for movable contact parts. The silver-coated composite material for movable contact parts according to claim 1, wherein the outermost layer has a thickness of 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, wherein the contact part is formed in a dome shape or a convex shape. parts.

Images