Electrical contact member and manufacturing method thereof

Abstract

The present invention provides an electrical contact member having a multilayer graphene film or a multilayer graphene oxide film on a conductive base material, in which the surface of the multilayer graphene film or the multilayer graphene oxide film has high adhesion and corrosion resistance and a low coefficient of friction, and a method for manufacturing the same. [Solution] An electrical contact member has a multilayer graphene film or a multilayer graphene oxide film on a conductive base material, and the upper limit of the friction coefficient when a scratch test is performed on the surface of the multilayer graphene film or the multilayer graphene oxide film is 0.25 or less, and a method for manufacturing an electrical contact member includes a step of forming the multilayer graphene film or the multilayer graphene oxide film on the conductive base material and then performing a pressure treatment on the surface of the multilayer graphene film or the multilayer graphene oxide film.

Description

[Technical Field]

[0001] The present invention relates to an electrical contact member and a method for manufacturing the same. [Background technology]

[0002] Electrical contact components such as connectors are required to have high contact reliability with mating terminals and high wear resistance at the connection portion with the mating terminal. Therefore, connector contact portions are generally plated with precious metals such as gold, silver, and tin. However, the use of expensive precious metal plating tends to increase the production cost of connectors. Therefore, forming a graphene film on the contact portion (terminal contact) of a connector instead of a precious metal plating layer has been proposed. Graphene film is a monoatomic film composed of carbon atoms and has excellent electrical conductivity and chemical stability, so it has attracted attention as a new, highly reliable terminal contact material. Various methods for forming graphene films on the surfaces of various components have been proposed (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-123733 Summary of the Invention [Problem to be solved by the invention]

[0004] The graphene film described above is fabricated by stacking multiple layers using, for example, electrophoretic deposition. In this case, the graphene film adheres to the substrate (conductive base material) of the connector terminal, such as a copper alloy, through van der Waals forces. However, because the adhesion force due to van der Waals forces depends on the distance to the object, there is a concern that variations in the gap between the substrate and the graphene film or gaps due to the overlapping of materials may result in partial poor adhesion at a microscopic level. Furthermore, variations in the gaps in the membrane structure reduce the hardness of the membrane surface, resulting in a higher coefficient of friction, which is important when inserting a connector. Furthermore, microscopic gaps can cause pinholes, which can lead to poor coating performance and reduced corrosion resistance. Although the above has been described with respect to multilayer graphene films, similar problems also exist with multilayer graphene oxide films.

[0005] The present invention has been made in view of the problems inherent in the conventional techniques, and an object of the present invention is to provide an electrical contact member having a multilayer graphene film or a multilayer graphene oxide film on a conductive base material, in which the surface of the multilayer graphene film or the multilayer graphene oxide film has high adhesion and corrosion resistance and a low coefficient of friction, and a method for manufacturing the same. [Means for solving the problem]

[0006] An electrical contact member according to an embodiment of the present invention has a multilayer graphene film or a multilayer graphene oxide film on a conductive base material, and the upper limit of the coefficient of friction when a scratch test is performed on the surface of the multilayer graphene film or the multilayer graphene oxide film is 0.25 or less.

[0007] In addition, a manufacturing method of an electrical contact member according to an aspect of the present invention includes a step of forming a multilayer graphene film or a multilayer graphene oxide film on a conductive base material, and then performing a pressure treatment on the surface of the multilayer graphene film or the multilayer graphene oxide film. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide an electrical contact member having a multilayer graphene film or a multilayer graphene oxide film on a conductive base material, in which the surface of the multilayer graphene film or the multilayer graphene oxide film has high adhesion and corrosion resistance and a low coefficient of friction, and a method for manufacturing the same. [Brief explanation of the drawings]

[0009] [Figure 1]FIG. 2 is a front view showing an example of the electrical contact member of the present embodiment. [Figure 2] FIG. 2 is a plan view of the electrical contact member shown in FIG. [Figure 3] FIG. 1 is a schematic diagram showing how a graphene oxide film is formed on the surface of a conductive base material by electrophoretic deposition. [Figure 4] 1 is a laser microscope image (height and width image) of the surface of the multilayer graphene oxide film formed in Example 1. [Figure 5] 1 is a laser microscope image (height and width image) of the surface of a multilayer graphene oxide film formed in Comparative Example 1. [Figure 6A] 1 is a photograph showing an indentation after a scratch test performed on the multilayer graphene oxide film formed in Example 1. [Figure 6B] 1 is a photograph showing an indentation after a scratch test performed on a multilayer graphene oxide film formed in Comparative Example 1. [Figure 7] 1 is a graph showing the friction coefficient versus the coordinates on the surface of a multilayer graphene oxide film in Example 1 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an electrical contact member and a method for manufacturing the same according to the present embodiment will be described in detail with reference to the drawings. Note that the dimensional proportions in the drawings are exaggerated for the sake of convenience and may differ from the actual proportions.

[0011] <Electrical contact materials> The electrical contact member of this embodiment has a multilayer graphene film or a multilayer graphene oxide film on a conductive base material, and the upper limit of the coefficient of friction when a scratch test is performed on the surface of the multilayer graphene film or the multilayer graphene oxide film is 0.25 or less. The scratch test was performed using a tribology tester (UMT-TriboLab). Specifically, a silver-plated copper alloy indenter with a tip radius r = 1 mm was used, and the indenter was slid over a length L = 0.5 mm on the multilayer graphene oxide film or the multilayer graphene oxide film surface while applying a load from 0.05 N to 0.1 N at a speed of 10 μm / s, and the friction coefficient was measured. In this embodiment, the multilayer graphene film and the multilayer graphene oxide film were composed only of graphene and graphene oxide, respectively.

[0012] The electrical contact member of this embodiment can reduce the upper limit of the coefficient of friction on the surface of the multilayer graphene film or multilayer graphene oxide film to 0.25 or less. Furthermore, pinholes (a state where the film is not completely covered due to microscopic gaps) and a decrease in corrosion resistance are suppressed. The upper limit of the coefficient of friction is preferably 0.24 or less. The lower limit of the upper limit of the coefficient of friction is not particularly limited.

[0013] In this embodiment, the thickness of the multilayer graphene film or multilayer graphene oxide film is preferably 1 to 50 nm, more preferably 1 to 10 nm. When the thickness is 10 nm or more, the increased thickness can be expected to improve wear resistance, and the film can be used as a sliding member with low friction, in addition to electrical contacts.

[0014] As an example of an electrical contact member of this embodiment, a male electrical contact member will be described with reference to the drawings. Fig. 1 is a front view of the male electrical contact member. Fig. 2 is a plan view of the electrical contact member shown in Fig. 1. As shown in Figs. 1 and 2, an electrical contact member 100 has a connecting portion 110 for mating with a female electrical contact member (not shown), and a crimping portion 112 for connecting to the connecting portion 110 and crimping an electric wire 210. In this embodiment, the electrically conductive member is the connecting portion 110.

[0015] The connection part 110 of the electrical contact member 100 is a plate-shaped member made of a metal base material having electrical conductivity. Examples of the electrically conductive material used for the connection part 110 include at least one metal selected from the group consisting of copper, copper alloy, aluminum, aluminum alloy, iron, iron alloy, magnesium, and magnesium alloy.

[0016] A terminal contact 115 made of a multilayer graphene film or a multilayer graphene oxide film is formed on at least a portion of the surface of the connecting portion 110 of the electrical contact member 100. The terminal contact 115 is made of a multilayer graphene film or a multilayer graphene oxide film, and when mated with a female electrical contact member, it comes into contact with the terminal contact of the electrical contact member. Here, "at least a portion of the surface of the connecting portion 110" means at least a portion of the surface that makes up the connecting portion 110 and that comes into contact with the terminal contact of the electrical contact member when mated with a female electrical contact member.

[0017] The terminal contacts 115 of the electrical contact member 100 are configured to be physically and electrically connected to the terminal contacts of the female electrical contact member when the male electrical contact member 100 and the female electrical contact member are mated.

[0018] The crimping portion 112 of the electrical contact member 100 is a member for crimping the electric wire 210 to the electric contact member 100, and is provided to connect to the connecting portion 110. The electric wire 210 is composed of a conductor 211 made of a conductive material and an electric wire coating material 212 that coats the conductor 211. The crimping portion 112 includes a conductor crimping portion 112a that crimps the conductor 211, and a coating material crimping portion 112b that crimps the electric wire coating material 212. Of the crimping portion 112 of the electric contact member 100, at least the conductor crimping portion 112a is made of a conductive material. The conductive material may be, for example, the same material as that used for the connecting portion 110 of the electric contact member 100.

[0019] Examples of conductive materials used for the conductor 211 constituting the electric wire 210 include copper, copper alloys, aluminum, and aluminum alloys. Among these, aluminum and aluminum alloys are preferred because they can reduce the weight of the conductor 211 and the electric wire 210.

[0020] The material used for the wire coating material 212 constituting the wire 210 is, for example, a resin that can ensure electrical insulation. As this resin, for example, an olefin-based resin or a resin whose main component is polyvinyl chloride (PVC) is used. Here, the main component refers to a component that accounts for 50% by mass or more of the entire wire coating material 212. As the olefin-based resin, for example, a resin made of one or more selected from the group consisting of polyethylene (PE), polypropylene (PP), ethylene copolymers, and propylene copolymers is used. Of these, resins whose main component is polypropylene (PP) or polyvinyl chloride (PVC) are preferred because of their high flexibility and durability.

[0021] The above electrical contact member can be manufactured by the manufacturing method of the electrical contact member of this embodiment described below.

[0022] <Method of manufacturing electrical contact member> The method for manufacturing an electrical contact member of this embodiment includes a step of forming a multilayer graphene film or a multilayer graphene oxide film on a conductive base material, and then applying pressure to the surface of the multilayer graphene film or the multilayer graphene oxide film.

[0023] In the method for manufacturing an electrical contact member according to this embodiment, a pressure treatment is applied to the surface of a multilayer graphene film or multilayer graphene oxide film formed on a conductive base material. This reduces variations in the gap between the conductive base material and the multilayer graphene film or the multilayer graphene oxide film, and reduces gaps due to the degree of material overlap. This prevents partial deterioration of adhesion. Furthermore, the variation in microscopic gaps in the film structure is reduced, improving the hardness of the film surface and resulting in a lower coefficient of friction. Furthermore, the occurrence of pinholes (a state where the film cannot be completely covered due to microscopic gaps) is suppressed, thereby reducing corrosion resistance.

[0024] In the method for manufacturing an electrical contact member of this embodiment, first, a multilayer graphene film or a multilayer graphene oxide film is formed on a conductive base material. The multilayer graphene film or the multilayer graphene oxide film can be formed by any of electrophoretic deposition, spray coating, and spin coating. The electrophoretic deposition method is described in detail below. Since the conductive base material has been described above, its description will be omitted here. The same description of the conductive base material applies to the method for manufacturing an electrical contact member of this embodiment.

[0025] Hereinafter, a method for forming a multilayer graphene oxide film on a conductive base material by electrophoretic deposition will be described. That is, the conductive base material is immersed in an aqueous dispersion containing graphene oxide, and a graphene oxide film is formed by electrophoretic deposition with the conductive base material serving as the anode. The multilayer graphene film can be obtained by reducing the multilayer graphene oxide film formed on the conductive base material.

[0026] Electrophoretic deposition is a technique used to form films on conductive base materials such as substrates. For example, it involves dispersing particles in water to prepare a dispersion, inserting an electrode (conductive base material) into the dispersion, and applying a voltage to cause the charged particles in the dispersion to migrate and deposit on the electrode. Because electrophoretic deposition does not require heat treatment and can be performed without vacuum and at room temperature, it allows for the easy and low-cost formation of graphene oxide films.

[0027] In this embodiment, when a graphene oxide film serving as a terminal contact is formed on the surface of a conductive base material by electrophoretic deposition, an aqueous dispersion containing graphene oxide having a negative zeta potential can be used. When electrophoretic deposition is performed with the conductive base material as the anode, the graphene oxide migrates toward the conductive base material on the anode side by electrophoresis and is deposited on the conductive base material. Furthermore, in the electrophoretic deposition method, the graphene oxide migrates due to Coulomb force generated by an external electric field and is firmly deposited on the surface of the conductive base material.

[0028] FIG. 3 shows an apparatus for performing a process by electrophoretic deposition in this embodiment. The apparatus shown in FIG. 3 includes an electrophoretic tank 30, an anode-side conductive base material 34 connected to the positive electrode of a power supply 38, and a cathode 36 connected to the negative electrode of the power supply 38. The electrophoretic tank 30 is filled with an aqueous dispersion 32 containing graphene oxide. When a voltage is applied from the power supply 38 to the anode-side conductive base material 34 and the cathode 36 to perform a process by electrophoretic deposition, graphene oxide, which has a negative zeta potential, migrates toward the anode-side conductive base material 34. Due to this behavior, graphene oxide is deposited on the surface of the conductive base material 34 to form a film.

[0029] Before forming a graphene oxide film on the conductive base material, it is preferable to remove the oxide film from the surface of the conductive base material. The method for removing the oxide film is not particularly limited, and the oxide film may be removed physically by polishing or chemically using a chemical solution. The chemical solution can be appropriately selected depending on the properties of the oxide film. The chemical solution may be, for example, an acidic solution such as sulfuric acid, hydrochloric acid, or nitric acid.

[0030] Before forming a graphene oxide film on the conductive base material, the surface of the conductive base material may be smoothed. The method for smoothing the surface of the conductive base material is not particularly limited, and the surface of the conductive base material may be smoothed by polishing, for example. Among polishing methods, chemical mechanical polishing is preferred for smoothing the surface of the conductive base material. Chemical mechanical polishing (CMP) is a method in which a chemical solution such as an acid or base is applied to the surface of the conductive base material, and the surface of the conductive base material is mechanically polished with abrasive particles, etc., to smooth the surface of the conductive base material. CMP can modify the surface of the conductive base material using a chemical solution to make it easier to polish, facilitating mechanical polishing and resulting in a smooth and excellent surface finish.

[0031] In this embodiment, the concentration of graphene oxide in the aqueous dispersion is preferably 0.001 to 0.1 mass %, and more preferably 0.005 to 0.01 mass %, from the viewpoint of forming a graphene oxide film with an appropriate thickness.

[0032] In addition to graphene oxide, a pH buffer solution, a preservative, etc. may be added to the aqueous dispersion.

[0033] The aqueous dispersion containing graphene oxide can be prepared by adding graphene oxide to a measured amount of water. The aqueous dispersion may be prepared by dispersing graphene oxide in water, or may be a commercially available graphene oxide dispersion.

[0034] In this embodiment, as described above, by electrophoretic deposition, graphene oxide migrates due to Coulomb force generated by an external electric field and is firmly deposited on the surface of a conductive base material. Therefore, the adhesion of graphene oxide can be adjusted by the Coulomb force. Here, when the external electric field is E (V / m) and the electrolysis is Q (C), the Coulomb force F (N) is given by F = QE. That is, the Coulomb force acting on graphene oxide in an aqueous dispersion can be controlled by the applied voltage or the charge of graphene oxide. Furthermore, the charge of graphene oxide can be adjusted by the zeta potential, i.e., the pH of the aqueous dispersion. Therefore, increasing the Coulomb force to improve the adhesion of the graphene oxide film to the conductive base material can be achieved by increasing the applied voltage and / or decreasing the pH of the aqueous dispersion.

[0035] For these reasons, it is preferable that the voltage applied to each of the anode and cathode electrodes is 1 to 100 V. In the electrophoresis tank, the distance between each of the anode and cathode electrodes can be set appropriately.

[0036] The voltage application time varies depending on the voltage, but is preferably 0.1 to 4 minutes. By setting the application time to 0.1 minutes or more, a good graphene oxide film can be formed on the conductive base material. Furthermore, by setting the application time to 4 minutes or less, the thickness of the graphene oxide film can be reduced. The voltage application time is more preferably 1 minute or more. Furthermore, the voltage application time is more preferably 3 minutes or less. Note that the longer the voltage application time, the thicker the graphene oxide film.

[0037] As described above, after forming a graphene oxide film on a conductive base material, the graphene oxide constituting the graphene oxide film can be reduced to form a reduced graphene oxide film. That is, since graphene oxide is a nonconductor, it is reduced to become a conductor so that it can be suitably used as a contact for an electrical contact member.

[0038] The method for reducing graphene oxide is not particularly limited as long as it can reduce the oxygen-containing functional groups of graphene oxide, and examples thereof include a method of performing heat treatment under a reducing atmosphere (thermal reduction method), a method of using a reducing agent such as hydrazine or sodium borohydride (chemical reduction method), a hydrothermal method, and a method of irradiating with electromagnetic waves such as microwaves and lasers.

[0039] Although the method for forming a multilayer graphene oxide film by electrophoretic deposition has been described above, the multilayer graphene oxide film may also be formed by spray coating or spin coating. Known techniques can be used for both the spray coating and spin coating methods.

[0040] In this embodiment, a pressure treatment is applied to the surface of the multilayer graphene film or multilayer graphene oxide film obtained as described above. A multilayer graphene oxide film formed by electrophoretic deposition is formed by the electrical attraction between an applied voltage and the zeta potential of the raw materials dispersed in the solution. Therefore, depending on the stacking state of the raw materials, there are microscopically rough portions in the film thickness direction. Therefore, a pressure treatment is applied to the surface of the obtained multilayer graphene film or multilayer graphene oxide film to promote densification of the film and reduce gaps within the multilayer structure or between the conductive base material and the multilayer graphene film or multilayer graphene oxide film.

[0041] The pressure treatment can be carried out using a pressure jig that is flat or shaped to fit the contact shape. Examples of such pressure jigs include pressure rollers and metal blocks with smooth surfaces, and materials with hardness equal to or greater than that of the base metal. For example, a copper alloy base material can be pressed with a stainless steel block. In particular, when pressure rollers are used, continuous production is possible by sandwiching a conductive base material on which a multilayer graphene film or a multilayer graphene oxide film has been formed between the pressure rollers and rotating and pressing them.

[0042] In the pressure treatment, the pressure applied to the surface of the multilayer graphene film or the multilayer graphene oxide film is 20 to 500 N / mm2 It is preferable that the pressure is 20 to 500 N / mm 2 By doing so, the effects of the manufacturing method of this embodiment (adhesion, corrosion resistance, low coefficient of friction) can be efficiently exhibited.

[0043] In the pressure treatment, it is preferable to heat the surface of the multilayer graphene film or the multilayer graphene oxide film. The surface of the multilayer graphene film or the multilayer graphene oxide film can be heated, for example, by heating the pressure jig used during pressure application. By simultaneously applying pressure and heating, unnecessary residual solvent during film formation can be removed. This is particularly effective for multilayer graphene oxide, as its electrical conductivity is improved by thermal reduction. When heating, the heating temperature is preferably 40 to 400°C. Furthermore, since the pressurized portion is in close contact with the multilayer graphene film or the multilayer graphene oxide film, heating and reduction can be performed in a low oxygen concentration state even in a processing device in an air atmosphere, improving reduction efficiency. [Example]

[0044] Hereinafter, the present embodiment will be described in more detail with reference to examples and comparative examples, but the present embodiment is not limited to these examples.

[0045] [Example 1] Graphene oxide was added to water to a concentration of 4 mg / L to prepare a graphene oxide dispersion. A conductive base material (a copper alloy plated with 3 μm of silver) was inserted as the anode into the electrophoresis tank containing the dispersion, and a conductive base material similar to the anode was inserted as the cathode. The cathode and anode were fixed in the electrophoresis tank so that the interelectrode distance between them was 10 mm. The cathode and anode were then connected to a DC power supply, and a DC voltage of 3 V was applied between the cathode and anode for 3 minutes. In this way, a 1 μm-thick graphene oxide film was deposited on the surface of the conductive base material on the anode side by electrophoretic deposition, producing a test sample.

[0046] The graphene oxide film obtained as described above was subjected to a surface pressure of 100 N / mm using a pressure jig made of a 10 mm square aluminum block coated with PTFE (polytetrafluoroethylene) resin, using an Instron compression tester. 2 The pressure treatment was carried out.

[0047] [Comparative Example 1] A test sample was prepared by depositing a graphene oxide film in the same manner as in Example 1, except that the pressure treatment was not performed.

[0048] 4 and 5 show laser microscope images (height and width images) of the graphene oxide films obtained in Example 1 and Comparative Example 1. A comparison of Fig. 4 and Fig. 5 reveals that the surface of the graphene oxide film obtained in Example 1 is denser than the surface of the graphene oxide film obtained in Comparative Example 1.

[0049] Meanwhile, the centerline surface roughness Sa of the graphene oxide films obtained in Example 1 and Comparative Example 1 was measured using a KEYENCE VK-X1100. The measurement results showed that the centerline surface roughness Sa of the graphene oxide film surface of Comparative Example 1 was 0.27 μm, while the centerline surface roughness Sa of the graphene oxide film surface of Example 1 was 0.24 μm. This also shows that the surface of the graphene oxide film obtained in Example 1 is denser than the surface of the graphene oxide film obtained in Comparative Example 1.

[0050] Next, a scratch test was performed on the graphene oxide films obtained in Example 1 and Comparative Example 1. The scratch test was performed using a tribology testing machine (UMT-TriboLab) by applying a load from 0.05 N to 0.1 N at a speed of 10 μm / s while sliding for a length L of 0.5 mm. The indentations produced by the scratch test are shown in FIG. 6A for Example 1 and in FIG. 6B for Comparative Example 1. From FIGS. 6A and 6B, it can be seen that Example 1 had fewer indentations than Comparative Example 1, and film peeling was suppressed. Therefore, it can be seen that the graphene oxide film of Example 1 has superior adhesion strength to the graphene oxide film of Comparative Example 1.

[0051] The friction coefficients of the multilayer graphene oxide film surfaces in Example 1 and Comparative Example 1 were measured using a tribology tester (UMT-TriboLab) under the following measurement conditions. The measurement results for Example 1 and Comparative Example 1 are shown in a graph in Figure 7, which plots the friction coefficients against the coordinates. (Measurement conditions) Sliding length L=0.5mm Load: 0.05 to 0.1 N (sliding while applying load at a speed of 10 μm / s)

[0052] 7, it can be seen that Example 1 has a lower friction coefficient than Comparative Example 1. This is presumably because the densification of the film increases hardness, thereby reducing the friction coefficient.

[0053] The comparison between Example 1 and Comparative Example 1 above shows that the manufacturing method of this embodiment can provide an electrical contact member having high adhesion and corrosion resistance on the surface of a multilayer graphene film or a multilayer graphene oxide film and a low friction coefficient.

[0054] Although the present embodiment has been described above, the present embodiment is not limited to this, and various modifications are possible within the scope of the gist of the present embodiment. [Explanation of symbols]

[0055] 30 Electrophoresis tank 32 Aqueous dispersion 34 Conductive base material (anode) 36 cathode 38 Power supply 100 Electrical contact member 110 Connection 115 Terminal Contact

Claims

1. A multilayer graphene film or a multilayer graphene oxide film is provided on a conductive base material, an upper limit value of a coefficient of friction when a scratch test is performed on a surface of the multilayer graphene film or the multilayer graphene oxide film is 0.25 or less;

2. 2. The electrical contact member according to claim 1, wherein the multilayer graphene film or the multilayer graphene oxide film has a thickness of 1 nm to 50 nm.

3. 2. A method for manufacturing an electrical contact member according to claim 1, comprising the steps of: A method for manufacturing an electrical contact member, comprising the steps of forming the multilayer graphene film or the multilayer graphene oxide film on the conductive base material, and then applying pressure to a surface of the multilayer graphene film or the multilayer graphene oxide film.

4. In the pressure treatment, a pressure applied to the surface of the multilayer graphene film or the multilayer graphene oxide film is 20 to 500 N / mm ２ The method for producing an electrical contact member according to claim 3, wherein

5. The method for manufacturing an electrical contact member according to claim 3 or 4, wherein the multilayer graphene film or the multilayer graphene oxide film is formed by any one of an electrophoretic deposition method, a spray coating method, and a spin coating method.

6. The method for manufacturing an electrical contact member according to claim 3 or 4, wherein the surface of the multilayer graphene film or the multilayer graphene oxide film is heated during the pressure treatment.

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