JP7498908B2 - Electrical contact member and method for producing same - Google Patents

Description

The present invention relates to an electrical contact member and a method for manufacturing the same.

In recent years, as part of international efforts to protect the environment, it has become necessary to reduce carbon dioxide ( _CO2 ), a greenhouse gas. The Japanese government has also formulated a green growth strategy for "carbon neutral by 2050," and technology to reduce _CO2 is required in 14 fields where growth is expected. As a result, IoT and DX are being promoted, and demand for electric and electronic parts is increasing. In addition, the use of hydrogen fuel cells is expected to expand as a battery that does not generate _CO2 .

In this environment, Au plating, which has low contact resistance and is chemically stable under high temperature and humidity conditions, is used for surface treatment of electrical contacts used in electrical and electronic components and hydrogen fuel cells. However, due to the high cost of Au itself, a cheaper surface treatment to replace Au plating is desired. Noble metal plating such as Pd and Ru has been considered as an alternative to Au plating, but the contact resistance, chemical stability, and production costs were insufficient.

To solve the above issues of production costs and low contact resistance, composite plating that incorporates conductive materials such as carbon into the plated metal is being considered.

Patent Document 1 proposes composite plating containing graphite in Sn, Ag or alloys thereof for use in terminals, connectors and switch materials for electronic components.

Patent Document 2 proposes a surface-treated steel sheet for battery cases in which a graphite-dispersed nickel plating layer containing dispersed graphite is formed on at least the surface that faces the inside of the battery case.

In Non-Patent Document 1, graphite is compounded in electroless Ni-B plating, and the hardness, friction and wear properties, and contact electrical resistance of the film are examined.

JP 2012-057212 A WO 00/05437

Surface Technology, Surface Finishing Association of Japan, 1993, Vol. 44, No. 11, pp. 961-965

However, in the past, the chemical stability of composite plating films had not been fully studied. In particular, no attention was paid to contact resistance under high temperature and high humidity conditions, and contact resistance under high temperature and high humidity conditions had not been fully studied.

In this situation, the present invention aims to provide an electrical contact member having a composite nickel plating film that has low contact resistance and is chemically stable, and a method for manufacturing the same.

As a result of intensive research aimed at solving the above problems, the present inventors discovered that the following invention meets the above object, and thus completed the present invention.
That is, the present invention relates to the following inventions.

<1> An electrical contact member comprising: an object to be plated; and a composite nickel plating film formed on the object to be plated, wherein the composite nickel plating film contains nickel or a nickel alloy, and conductive carbon particles dispersed in the nickel or nickel alloy, and an area ratio of the conductive carbon particles on a surface of the composite nickel plating film is 20 area % or more.
<2> The electrical contact member according to <1>, wherein a content of the conductive carbon particles on the surface of the composite nickel plating film is 10 mass % or more.
<3> The electrical contact member according to <1> or <2>, wherein the nickel or nickel alloy is a nickel-phosphorus alloy containing nickel and phosphorus.
<4> The electrical contact member according to any one of <1> to <3>, wherein the conductive carbon particles are graphite.
<5> The electrical contact member according to any one of <1> to <4>, wherein the object to be plated has a conductive base material and a base metal layer formed on the conductive base material, and the composite nickel plating film is formed on the base metal layer.

<6> A method for manufacturing an electrical contact member, comprising: a first step of immersing an object to be plated and an anode in an aqueous dispersion containing conductive carbon particles and a cationic surfactant, and applying a voltage between the object to be plated and the anode to deposit the conductive carbon particles on a surface of the object to be plated; and a second step of performing an electroless plating process on the object to be plated, on whose surface the conductive carbon particles have been deposited, to deposit nickel or a nickel alloy, thereby forming a composite nickel plating film on the object to be plated, which contains the nickel or nickel alloy and the conductive carbon particles.
<7> The method for manufacturing an electrical contact member according to <6>, wherein the object to be plated has a conductive base material and a base metal layer formed on the conductive base material, and in the first step, the conductive carbon particles are deposited on a surface of the base metal layer.

The present invention provides an electrical contact member having a composite nickel plating film that has low contact resistance and is chemically stable, and a method for manufacturing the same.

1 is a schematic diagram of an electrical contact member according to the present invention; 1 is a schematic diagram of an electrical contact member according to the present invention; 1 is a SEM image of a cross section of a specimen of Example 1. 1 is an SEM image of the surface of the plating film of a specimen of Example 1. 1 is an SEM image of the surface of the plating film of a specimen of Example 2. 1 is an SEM image of the surface of the plating film of a specimen of Example 3. 1 is an SEM image of the surface of the plating film of a specimen of Comparative Example 1. 1 is an SEM image of the surface of the plating film of a specimen of Comparative Example 2.

The following describes in detail the embodiments of the present invention, but the description of the constituent elements described below is one example (representative example) of the embodiment of the present invention, and the present invention is not limited to the following content as long as the gist of the invention is not changed. Note that when the expression "~" is used in this specification, it is used as an expression including the numerical values or physical property values before and after it.

<Electrical Contact Member>
The present invention relates to an electrical contact member (hereinafter sometimes referred to as "the electrical contact member of the present invention") which has a plated object and a composite nickel plating film formed on the plated object, wherein the composite nickel plating film contains nickel or a nickel alloy and conductive carbon particles dispersed in the nickel or nickel alloy, and the area ratio of the conductive carbon particles on the surface of the composite nickel plating film is 20 area % or more.

<Method of Manufacturing Electrical Contact Member>
The present invention relates to a method for producing an electrical contact member (hereinafter, sometimes referred to as the "method for producing an electrical contact member of the present invention") which comprises: a first step of immersing an object to be plated and an anode in an aqueous dispersion containing conductive carbon particles and a cationic surfactant and applying a voltage between the object to be plated and the anode to deposit conductive carbon particles on the surface of the object to be plated; and a second step of performing an electroless plating process on the object to be plated, on whose surface the conductive carbon particles have been deposited, to deposit nickel or a nickel alloy, thereby forming a composite nickel plating film on the object to be plated, containing nickel or a nickel alloy and conductive carbon particles (hereinafter, may be referred to as the "method for producing an electrical contact member of the present invention").

The present inventors focused on the amount of conductive carbon particles exposed on the surface of the plating film. Conductive carbon particles have high chemical stability and are less likely to oxidize than metals, so they conducted intensive research, thinking that by forming a structure in which conductive carbon particles are exposed at a high density on the surface of the plating film, a composite plating film in which contact resistance is less likely to increase even in a high-temperature, high-humidity environment can be obtained. However, when electroless plating was performed using a plating bath in which conductive carbon particles were dispersed in advance, the amount of conductive carbon particles taken up into the plating film was small, and a structure in which conductive carbon particles are exposed at a high density on the plating film surface was not obtained. It was found that increasing the amount of conductive carbon particles added to the plating bath in order to increase the amount of conductive carbon particles taken up into the plating film causes problems such as aggregation and precipitation. In addition, it was found that in a method of electrolytic plating using a plating bath in which conductive carbon particles are dispersed, plating grows on the conductive carbon particles in contact with the plating film, resulting in protruding plating, and the conductive carbon particles are less likely to be exposed on the surface of the plating film. Therefore, even if the amount of conductive carbon particles taken up into the plating film is increased, it is difficult to increase the amount of conductive carbon particles on the surface of the plating film.

As a result of further research, it was found that a structure with a high density of conductive carbon particles exposed on the surface of the plating film can be obtained by depositing graphite at a high density on the surface of the cathode by electrophoresis in an aqueous solution in which conductive carbon particles are dispersed using a cationic surfactant, and then forming a plating film while filling the gaps between the conductive carbon particles with nickel alloy deposited by electroless plating. It was also found that this structure is less susceptible to an increase in contact resistance even in high-temperature, high-humidity tests. The present invention is based on these findings.

As the surface oxidation of nickel or nickel alloy progresses, the conductive carbon particles become conductive paths because nickel oxide has high resistance. If there are too few conductive carbon particles on the surface of the composite nickel plating film, the conductive paths are reduced, and the resistance is likely to increase due to the surface oxidation of the nickel or nickel alloy. In particular, under high temperature and high humidity, the surface of nickel or nickel alloy is easily oxidized, and the resistance is likely to increase. The electrical contact member of the present invention has a structure in which the area ratio of conductive carbon particles on the surface of the composite nickel plating film is 20 area % or more, and conductive carbon particles, which are highly chemically stable and less likely to be oxidized than metals, are exposed at a high density on the surface. Therefore, the contact resistance is low and the chemical stability is excellent. Such an electrical contact member of the present invention can be suitably obtained by the manufacturing method of the electrical contact member of the present invention.

In particular, the electrical contact member of the present invention is unlikely to increase in contact resistance even under high temperature and high humidity conditions, and has excellent chemical stability.

The electrical contact member of the present invention and the manufacturing method of the electrical contact member of the present invention will be described in more detail below.

<Electrical Contact Member>
Fig. 1 is a schematic diagram showing an example of an electrical contact member of the present invention. As shown in Fig. 1, the electrical contact member 1 has a composite nickel plating film 10 containing nickel or nickel alloy 12 and conductive carbon particles 14 dispersed in the nickel or nickel alloy 12, and an object to be plated 20.

[Composite nickel plating film 10]
The composite nickel plating film 10 constituting the electrical contact member of the present invention is a film formed on an object to be plated 20, and is a film mainly composed of nickel or nickel alloy 12 and conductive carbon particles 14. The thickness of the composite nickel plating film 10 is appropriately selected depending on the size of the conductive carbon particles 14, the intended use, etc. For example, it can be 0.5 to 20 μm, 1 to 10 μm, or 1 to 5 μm. The thickness of the composite nickel plating film 10 is the plating thickness of the nickel or nickel alloy 12, and some of the conductive carbon particles 14 are exposed beyond this thickness.

(Nickel or Nickel Alloy 12)
The composite nickel plating film 10 includes nickel or a nickel alloy 12. Nickel or nickel alloy 12 has excellent hardness and abrasion resistance, is inexpensive, and can form a highly uniform film by utilizing electroless plating.

Nickel or nickel alloy 12 is nickel alone or an alloy mainly made of nickel containing nickel and elements other than nickel (containing 50% or more by mass of nickel). Examples of nickel alloys include nickel alloys containing nickel (Ni) and one or more selected from the group consisting of phosphorus (P), boron (B), cobalt (Co), manganese (Mn), iron (Fe), copper (Cu) and tin (Sn). Nickel or nickel alloy 12 is preferably a nickel alloy containing nickel, phosphorus and/or boron, and more preferably a nickel phosphorus alloy (NiP alloy) containing nickel and phosphorus. By containing phosphorus, the plating film has excellent corrosion resistance and the thickness of the surface oxide film is less likely to increase in a high-temperature and high-humidity environment.

(Conductive Carbon Particles 14)
The composite nickel plating film 10 contains conductive carbon particles 14. The conductive carbon particles 14 are dispersed in nickel or nickel alloy 12. A portion of the conductive carbon particles 14 is exposed on the surface of the composite nickel plating film 10, and the conductive carbon particles 14 are scattered (dispersed) on the surface of the composite nickel plating film 10.

Examples of conductive carbon particles 14 include graphite, graphene, carbon black, and carbon nanotubes. Among these, graphite is preferred because it is inexpensive, has low contact resistance, and is chemically stable.

Examples of graphite include natural graphite such as scaly graphite, flake graphite, spherical graphite, expanded graphite, expanded graphite, and earthy graphite, and artificial graphite, with artificial graphite being preferred.

The shape of the conductive carbon particles 14 is not particularly limited, but it is preferable that the conductive carbon particles 14 are non-spherical. By using non-spherical conductive carbon particles, the contact area can be increased, and the adhesive strength with the plated object can be increased. The spherical conductive carbon particles 14 tend to easily fall off from the plated object. Note that non-spherical refers to a shape other than a perfect sphere, such as a scale-like, needle-like, or amorphous shape. For example, the non-spherical conductive carbon particles 14 have a value of 1.2 or more (maximum diameter/minimum diameter>1.2) obtained by dividing the maximum diameter (major diameter) of the conductive carbon particles by the minimum diameter (minor diameter).

The average particle size of the conductive carbon particles 14 is preferably 0.01 μm or more, more preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. The average particle size of the conductive carbon particles 14 is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less. If the conductive carbon particles 14 are too large, the thickness of the composite nickel plating film 10 becomes thick, which is uneconomical. If the conductive carbon particles 14 are too small, there will be many conductive carbon particles that are not connected to other conductive carbon particles, and the effect of the composite of nickel and carbon will not be exerted easily, and the chemical stability of the composite nickel plating film 10 under high temperature and high humidity tends to decrease. The particle size of the conductive carbon particles 14 is the diameter if the conductive carbon particles 14 are spherical, and is the maximum diameter if the conductive carbon particles 14 are non-spherical. The average particle size of the conductive carbon particles 14 can be determined, for example, from a cross-sectional image of the member taken by a scanning electron microscope (SEM), and can be calculated as the average value of 100 conductive carbon particles 14.

(Area ratio of conductive carbon particles 14 on the surface of composite nickel plating film 10)
The area ratio of the conductive carbon particles 14 on the surface of the composite nickel plating film 10 is 20 area% or more. Since the area ratio of the conductive carbon particles 14 on the surface of the composite nickel plating film 10 is high in this manner, the resistance is unlikely to increase, and the composite nickel plating film 10 has excellent chemical stability. The area ratio of the conductive carbon particles 14 on the surface of the composite nickel plating film 10 is preferably 30 area% or more, more preferably 35 area% or more. If the area ratio of the conductive carbon particles 14 on the surface of the composite nickel plating film 10 is too small, the chemical stability tends to decrease. In addition, there is no particular upper limit on the area ratio of the conductive carbon particles 14 on the surface of the composite nickel plating film 10, but it can be 90 area% or less, 80 area% or less, 70 area% or less, 60 area% or less, etc.

The area ratio of the conductive carbon particles 14 on the surface of the composite nickel plating film 10 is the ratio of the area of the conductive carbon particles 14 in a composition image (COMPO image) obtained by observing the surface of the composite nickel plating film 10 with a scanning electron microscope (SEM), and is a percentage obtained by dividing the total area of the conductive carbon particles 14 calculated by analyzing the composition image with image analysis software by the area of the entire composition image. Specifically, a composition image of the surface of the plating film is first obtained with a scanning electron microscope. The observation magnification may be adjusted according to the average particle size of the conductive carbon particles 14 so that the appropriate observation area is obtained. For example, a composition image (area 172 μm × 240 μm) is photographed at a magnification of 500 times. Next, the composition image is binarized with an EDX image analysis software (GENESIS Spectrum), and the area of the black area is calculated as the area of the conductive carbon particles 14. The area ratio of the conductive carbon particles 14 on the surface of the composite nickel plating film 10 can be calculated using the calculated total area of the black areas and the area of the entire composition image.

(Content of conductive carbon particles 14 on the surface of the composite nickel plating film 10)
The content of the conductive carbon particles 14 on the surface of the composite nickel plating film 10 is preferably 10% by mass or more, more preferably 15% by mass or more, and even more preferably 20% by mass or more. The upper limit is not particularly limited. From the viewpoint of durability, the content of the conductive carbon particles 14 on the surface of the composite nickel plating film 10 is preferably 90% by mass or less, and may be 80% by mass, 70% by mass or less, 60% by mass or less, 50% by mass or less, etc. The content of the conductive carbon particles 14 on the surface of the composite nickel plating film 10 is the mass ratio of the conductive carbon particles 14 to the total of the nickel or nickel alloy 12 and the conductive carbon particles 14 when measured by scanning electron microscope-energy dispersive X-ray analysis (SEM-EDX) at an acceleration voltage of 15 kV.

In the composite nickel plating film 10, the total of the nickel or nickel alloy 12 and the conductive carbon particles 14 is preferably 97% by mass or more, and more preferably 98% by mass or more. It is more preferable that the composite nickel plating film 10 is substantially composed of the nickel or nickel alloy 12 and the conductive carbon particles 14, but it may contain impurities that are inevitably contained in the manufacturing process or impurities that do not affect the physical properties. In addition, in the composite nickel plating film 10, it is preferable that the nickel or nickel alloy 12 is a nickel alloy containing nickel and phosphorus and/or boron, and the conductive carbon particles 14 are graphite. More preferably, the nickel or nickel alloy 12 is a nickel phosphorus alloy containing nickel and phosphorus, and the conductive carbon particles 14 are graphite.

One suitable composite nickel plating film 10 is a film containing 10-90% by mass of C, 11% or less by mass of P, 6% or less by mass of B, with the balance being Ni and unavoidable impurities. Another suitable composite nickel plating film 10 is a film containing 10-90% by mass of C, 1-11% by mass of P, with the balance being Ni and unavoidable impurities.

[Plating object 20]
The object to be plated 20 is not particularly limited, and various metal materials such as copper, aluminum, titanium, etc. can be used. The shape of the object to be plated 20 is not limited to a plate material, and it can be a shape suitable for the application, such as a wire material, a bar material, a tube material, a square material, or various component shapes.

Because it is easy to form a composite nickel plating film 10 on the object to be plated 20, it is preferable that the object to be plated 20 has a conductive base material and a base metal layer formed on the conductive base material.

Figure 2 is a schematic diagram of an electrical contact member 1a having a conductive substrate 22, a plated object 20a having a base metal layer 24 formed on the conductive substrate 22, and a composite nickel plating film 10 formed on the base metal layer 24. The electrical contact member 1a is the same as the electrical contact member 1 except for the configuration of the plated object 20a.

(Conductive substrate 22)
Examples of the conductive base material 22 include metal base materials such as copper, aluminum, titanium, etc. The shape of the conductive base material 22 is not particularly limited, and a base material suitable for the application can be appropriately selected and used.

(Base metal layer 24)
The base metal layer 24 is a layer formed on the surface of the conductive base material 22, and is a layer formed from a metal. The base metal layer 24 may be formed from a metal that can serve as a catalyst when forming the composite nickel plating film 10, and may be the same metal as the nickel or nickel alloy 12, or a different metal. When the metal constituting the base metal layer 24 is the same as the nickel or nickel alloy 12 constituting the composite nickel plating film 10, the base metal layer 24 and the composite nickel plating film 10 can be distinguished from each other by the presence or absence of conductive carbon particles.

The base metal layer 24 may be, for example, a layer of nickel, a nickel alloy, cobalt, a cobalt alloy, iron, or an iron alloy. From the viewpoint of corrosion resistance, the base metal layer 24 is preferably a layer of nickel or a nickel alloy. The nickel alloy may be a nickel alloy containing nickel (Ni) and one or more selected from the group consisting of phosphorus (P), boron (B), cobalt (Co), manganese (Mn), iron (Fe), copper (Cu), and tin (Sn).

The thickness of the base metal layer 24 is not particularly limited, but can be 10 nm or more, 100 nm or more, 1 μm or more, etc. The upper limit can be 100 μm or less, 50 μm or less, etc.

The plated object 20a, which has a conductive substrate 22 and a base metal layer 24 formed on the conductive substrate 22, can be obtained by plating the conductive substrate 22 using a known plating method so that the metal that constitutes the base metal layer 24 precipitates.

<Applications of electrical contact materials>
Specifically, the electrical contact member of the present invention can be used for terminals and connectors of electronic components, switch materials (relay terminals), battery cases, separators and current collectors of fuel cells, terminals of switchboards, bus bars, and the like.

<Method of Manufacturing Electrical Contact Member>
As described above, the method for manufacturing an electrical contact member of the present invention includes a first step of immersing an object to be plated and an anode in an aqueous dispersion containing conductive carbon particles and a cationic surfactant and applying a voltage between the object to be plated and the anode to deposit conductive carbon particles on the surface of the object to be plated, and a second step of performing an electroless plating process to deposit nickel or a nickel alloy on the object to be plated with the conductive carbon particles deposited on its surface, thereby forming a composite nickel plating film containing nickel or a nickel alloy and the conductive carbon particles on the object to be plated.

Conductive carbon particles can be deposited on the object to be plated by positively charging the conductive carbon particles with a cationic surfactant and applying a voltage so that the object to be plated becomes the cathode. By further performing electroless plating in this state, a composite nickel plating film with a high area ratio of conductive carbon particles on the film surface can be formed. By using such a method, it is possible to reduce variation in the thickness of the plating film and produce it with high reproducibility. Furthermore, the electrical contact member of the present invention can be suitably obtained by the manufacturing method of the electrical contact member of the present invention.

(First step)
The first step is to immerse an object to be plated and an anode in an aqueous dispersion containing conductive carbon particles and a cationic surfactant, and apply a voltage between the object to be plated and the anode to deposit conductive carbon particles on the surface of the object to be plated.

(Aqueous dispersion)
The aqueous dispersion contains conductive carbon particles and a cationic surfactant, and is a liquid in which the conductive carbon particles are dispersed in water. The presence of the cationic surfactant suppresses the aggregation of the conductive carbon particles, improving the dispersibility of the conductive carbon particles in the aqueous dispersion. In addition, by dispersing the conductive carbon particles using the cationic surfactant, the conductive carbon particles become positively charged, so that when a voltage is applied, the conductive carbon particles can be moved to the cathode side (the side of the object to be plated). This allows the conductive carbon particles to be deposited at a high density on the surface of the object to be plated. In addition, since it is aqueous, it has a small environmental impact and is practical.

The aqueous dispersion may contain components other than the conductive carbon particles and the cationic surfactant, so long as they do not inhibit the deposition of the conductive carbon particles on the substrate to be plated. For example, the aqueous dispersion may contain components that have a pH buffering effect, such as acetic acid, citric acid, tartaric acid, succinic acid, and their salts (sodium salts, potassium salts, magnesium salts).

(cationic surfactant)
The cationic surfactant is not particularly limited, and known ones can be used. For example, the cationic surfactant may be an ammonium salt type cationic surfactant (such as an alkyl trimethyl ammonium halide, a dialkyl dimethyl ammonium halide, or a benzyl dimethyl alkyl ammonium chloride), an amine type cationic surfactant (such as a monoalkyl amine salt, a dialkyl amine salt, or a trialkyl amine salt), a pyridinium type cationic surfactant, an imidazolium salt type cationic surfactant, or a phosphonium salt type cationic surfactant.

The concentration of the cationic surfactant in the aqueous dispersion is, for example, 0.01 to 20 g/L or 0.1 to 15 g/L.

(Conductive carbon particles)
As described above, the conductive carbon particles are preferably graphite. The concentration of the conductive carbon particles in the aqueous dispersion is, for example, 1 to 100 g/L, or 10 to 50 g/L.

(anode)
The anode is not particularly limited and may be appropriately selected depending on the object to be plated, etc. For example, a metal plate such as stainless steel, iron, aluminum, copper, etc. may be used.

(Application of voltage)
In the first step, the object to be plated and the anode are placed facing each other with a gap in the aqueous dispersion, and a voltage is applied between the object to be plated and the anode so that the object to be plated becomes the cathode. As a result, the conductive carbon particles move toward the object to be plated, and the conductive carbon particles are deposited on the surface of the object to be plated facing the anode. Note that if the conductive carbon particles are negatively charged and a voltage is applied so that the object to be plated becomes the anode, the surface of the object to be plated may be oxidized. For example, if a voltage is applied to a plated object having a nickel layer as a base metal layer so that the object to be plated becomes the anode, the nickel may be oxidized. In the first step, the conductive carbon particles are positively charged and a voltage is applied so that the object to be plated becomes the cathode, so that the surface of the object to be plated is also less likely to be oxidized.

The applied voltage and application time are not particularly limited and may be appropriately selected depending on the desired deposition amount of conductive carbon particles, etc. For example, the voltage can be 5 to 200 V, 5 to 100 V, 10 to 50 V, etc. Furthermore, if the voltage is within such a range, a constant current may be applied. The application time of the voltage or current is about 5 seconds to 10 minutes, or 10 seconds to 5 minutes.

(Second step)
The second step is a step of performing an electroless plating process to precipitate nickel or a nickel alloy on the plated object having conductive carbon particles deposited on its surface, thereby forming a composite nickel plating film containing nickel or a nickel alloy and conductive carbon particles on the plated object.

The precipitation of nickel or nickel alloy fixes the conductive carbon particles onto the object to be plated, and the gaps between the conductive carbon particles are filled with nickel or nickel alloy, forming a composite nickel plating film. Unlike electrolytic plating, electroless plating is not affected by current distribution, so a uniform film thickness can be formed. Furthermore, electroless plating does not precipitate nickel or nickel alloy on the conductive carbon particles, so the effect of forming a composite between nickel or nickel alloy and conductive carbon particles can be fully exerted. Furthermore, because nickel or nickel alloy precipitates to fill the gaps between the conductive carbon particles, nodules are less likely to precipitate.

On the other hand, with electrolytic plating, it is difficult to form a plating film with a uniform thickness, and nickel or nickel alloys can also be deposited on the conductive carbon particles, making it difficult to increase the area ratio of conductive carbon particles on the surface of the formed plating film, making it difficult to achieve the composite effect.

The electroless plating method can be a known method. The plating bath is not particularly limited as long as it can precipitate nickel as a main component, and a known electroless nickel plating bath containing nickel salt, reducing agent, complexing agent, and pH adjuster can be used. For example, a general electroless NiP plating bath or an electroless NiB plating bath can be appropriately selected. Depending on the phosphorus content in the plating film, electroless NiP plating baths include low phosphorus baths, medium phosphorus baths, high phosphorus baths, and the like, and these can be used. In addition, taking into account the composition of nickel or nickel alloy and the reactivity of the electroless plating reaction, a third component such as Cu or Sn may be added to these general plating baths, or a pH adjuster may be added to adjust the pH.

There are no particular limitations on the electroless plating conditions, but it is preferable that the pH of the plating bath is 3 to 5, the temperature of the plating bath is 50 to 90°C or 60 to 80°C, and the plating time is 10 to 120 minutes or 15 to 60 minutes, for example.

The electroless plating process is preferably carried out so that the area ratio of conductive carbon particles on the surface of the composite nickel plating film formed is 20 area % or more. Also, the electroless plating process is preferably carried out so that the content of conductive carbon particles on the surface of the composite nickel plating film formed is 10 mass % or more.

In the second step, the electroless plating process is preferably electroless nickel plating that deposits a nickel alloy containing nickel and phosphorus and/or boron, and more preferably electroless nickel phosphorus plating (electroless NiP plating) that deposits a nickel phosphorus alloy containing nickel and phosphorus. Electroless NiP plating is excellent in terms of uniform film thickness as a plating metal and stability of the plating bath, and can form a film that is more corrosion resistant than electrolytic nickel plating. By performing electroless NiP plating, a composite nickel plating film containing a nickel phosphorus alloy containing nickel and phosphorus and conductive carbon particles can be formed.

The method for manufacturing an electrical contact member of the present invention may include a step other than the first step and the second step. For example, a cleaning step may be provided between the first step and the second step.

The method for manufacturing an electrical contact member of the present invention preferably includes a step of removing conductive carbon particles whose gaps are not filled with nickel or nickel alloy after the second step. This allows a more stable film to be formed.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless the gist of the invention is changed.

1. Preparation of plating film (Example 1)
A copper plate (30 mm×40 mm) having a thickness of 1 mm was plated with Ni as a base treatment using a Watts bath to prepare a Ni-plated copper plate.
A cationic surfactant (benzyldimethyltetradecylammonium chloride, concentration 1 g/L) and graphite particles (concentration 40 g/L, manufactured by Itoh Graphite Industries Co., Ltd., AGB-5, average particle size 5 μm) were added to pure water and stirred, and an aqueous solution was prepared by inserting a SUS304 plate as an anode and a Ni-plated copper plate as a cathode into the aqueous solution, followed by electrolysis at 20 V for 30 seconds, whereby graphite particles were deposited on the cathode.
Next, after washing with running water, the gaps between the graphite particles were filled with NiP alloy by electroless plating reaction by immersing in electroless NiP plating solution (low phosphorus type) at 80° C. The electroless NiP plating solution used was a low phosphorus type electroless nickel plating solution (Top Nicoron LPH-LF, manufactured by Okuno Chemical Industries Co., Ltd.) adjusted to pH 4.0.
Next, excess graphite particles that did not fill the interparticle gaps were removed with a brush to obtain a specimen having a graphite composite electroless NiP alloy plating film (composite nickel plating film). The thickness of the graphite composite electroless NiP alloy plating film was 2 μm, and the P concentration in the graphite composite electroless NiP alloy plating film was 6.2 wt %.

Figure 3 shows a cross-sectional SEM image of the specimen obtained in Example 1, observed using a scanning electron microscope (JSM-7001F, manufactured by JEOL Ltd.).

Example 2
A copper plate (30 mm×40 mm) having a thickness of 1 mm was plated with Ni as a base treatment using a Watts bath to prepare a Ni-plated copper plate.
A cationic surfactant (benzyldimethyltetradecylammonium chloride, concentration 1 g/L) and graphite particles (concentration 40 g/L, manufactured by Itoh Graphite Industries Co., Ltd., AGB-5, average particle size 5 μm) were added to pure water and stirred, and an SUS304 plate was inserted as an anode and a Ni-plated copper plate as a cathode into the aqueous solution, which was then electrolyzed at 20 V for 30 seconds to deposit graphite particles on the cathode.
Next, after washing with running water, the gaps between the graphite particles were filled with NiP alloy by electroless plating reaction by immersing in electroless NiP plating solution (medium phosphorus type) at 80° C. The electroless NiP plating solution used was a medium phosphorus type electroless nickel plating solution (Top Nicoron SDB-LF, manufactured by Okuno Chemical Industries Co., Ltd.) adjusted to pH 4.0.
Next, excess graphite particles that did not fill the interparticle gaps were removed with a brush to obtain a specimen having a graphite composite electroless NiP alloy plating film (composite nickel plating film). The thickness of the graphite composite electroless NiP alloy plating film was 2 μm, and the P concentration in the graphite composite electroless NiP alloy plating film was 8.0 wt %.

Example 3
A specimen having a graphite composite electroless NiP alloy plating film (composite nickel plating film) was obtained in the same manner as in Example 2, except that the plating solution was changed from an electroless NiP plating solution (medium phosphorus type) to an electroless NiP plating solution (high phosphorus type) prepared by adjusting the pH of a high phosphorus type electroless nickel plating solution (manufactured by Okuno Chemical Industries, Top Nicoron SA-98-LF) to 4.0. The thickness of the graphite composite electroless NiP alloy plating film was 3 μm, and the P concentration in the graphite composite electroless NiP alloy plating film was 9.4 wt%.

(Comparative Example 1)
A copper plate (30 mm×40 mm) having a thickness of 1 mm was plated with Ni as a base treatment using a Watts bath to prepare a Ni-plated copper plate.
A medium phosphorus type electroless nickel plating solution (Top Nicoron SDB-LF, manufactured by Okuno Chemical Industries) was adjusted to pH 4.5, and a cationic surfactant (benzyl dimethyl tetradecyl ammonium chloride, concentration 0.1 g/L) and graphite particles (concentration 10 g/L, manufactured by Itoh Graphite Industries Co., Ltd., AGB-5, average particle size 5 μm) were added and stirred to prepare a solution, which was then immersed at 80° C. for 30 minutes to obtain a specimen having a graphite composite electroless NiP alloy plating film. The thickness of the graphite composite electroless NiP alloy plating film was 3 μm, and the P concentration in the graphite composite electroless NiP alloy plating film was 7.9 wt %.

(Comparative Example 2)
A 1 mm-thick copper plate (30 mm×40 mm) was plated with Ni to a thickness of 4 μm as a base treatment using a Watts bath to prepare a Ni-plated copper plate.
A medium phosphorus electroless nickel plating solution (Top Nicoron SDB-LF, manufactured by Okuno Chemical Industries) was adjusted to pH 4.5, and the specimen was immersed at 80° C. for 30 minutes to obtain an electroless NiP alloy plating film. The thickness of the electroless NiP alloy plating film was 4 μm, and the P concentration in the electroless NiP alloy plating film was 8.9 wt %.

2. Evaluation (graphite content)
The surfaces of the test materials of Examples 1 to 3 and Comparative Examples 1 and 2 (observation magnification × 100, area 940 μm × 1200 μm) were observed at three locations with a scanning electron microscope (JSM-7001F manufactured by JEOL Ltd.) at an acceleration voltage of 15 kV, and were measured with EDX (GENESIS manufactured by AMETEK Co., Ltd.), and the average graphite content (wt%) was calculated from the weight ratios of C, Ni, and P by the ZAF method using analysis software (GENESIS Spectrum). The results are shown in Table 1.

(Graphite area ratio)
The surfaces of the test materials of Examples 1 to 3 and Comparative Examples 1 and 2 were observed with a scanning electron microscope (JSM-7001F manufactured by JEOL Ltd.) at an acceleration voltage of 15 kV, and composition images (COMPO images) of the surfaces (observation magnification ×500, area 172 μm × 240 μm) were photographed. The images were binarized with image analysis software (GENESIS Spectrum) for EDX (GENESIS manufactured by AMETECH Co., Ltd.), and the total area of the graphite particles in the image was divided by the area of the entire image to obtain the area ratio of the graphite particles.
4 to 8 show SEI images and composition images (COMPO images) of Examples 1 to 3 and Comparative Examples 1 and 2. Table 1 shows the calculated area ratios of graphite particles.

(Contact resistance)
The contact resistance of the surface of the test material was measured at five points by a two-probe method using a resistivity meter (Loresta EP manufactured by Mitsubishi Chemical Corporation), and the average value was calculated. The results are shown in Table 1.

(Moisture resistance)
To evaluate the moisture resistance, a pressure cooker test (PCT) was performed in which the samples were held at 150° C. and 98% RH for 240 hours, and then the contact resistance was evaluated. The results are shown in Table 1.

Visual observation of the specimens of Examples 1 to 3 revealed that the graphite composite electroless NiP alloy plating film of the specimens of Examples 1 to 3 was formed uniformly with little variation. In addition, when experiments similar to those of Examples 1 to 3 were performed except that the Ni-plated copper plate was replaced with a Ni-plated aluminum alloy plate (material A5052, thickness 3 mm) on which Ni plating was applied on a 50 mm x 50 mm aluminum alloy plate, a graphite composite electroless NiP alloy plating film was formed uniformly with little variation. It was found that the manufacturing method of the electrical contact member of the present invention can form a uniform plating film even when the size of the plated object is large.

The electrical contact member and its manufacturing method of the present invention can be used in the fields of electrical and electronic equipment and fuel cells, and are therefore industrially useful.

REFERENCE SIGNS LIST 1, 1a Electrical contact member 10 Composite nickel plating film 12 Nickel or nickel alloy 14 Conductive carbon particles 20, 20a Object to be plated 22 Conductive substrate 24 Undercoat metal layer

Claims (2)

a first step of immersing an object to be plated and an anode in an aqueous dispersion containing conductive carbon particles and a cationic surfactant, and applying a voltage between the object to be plated and the anode to deposit the conductive carbon particles on a surface of the object to be plated;
a second step of performing an electroless plating process on the plated object having the conductive carbon particles deposited on its surface to deposit nickel or a nickel alloy, thereby forming a composite nickel plating film on the plated object containing the nickel or nickel alloy and the conductive carbon particles. The object to be plated has a conductive base material and a base metal layer formed on the conductive base material,
The method for producing an electrical contact member according to claim 1 , wherein in the first step, the conductive carbon particles are deposited on a surface of the base metal layer.

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