Contact materials

Abstract

The objective is to provide a contact material that suppresses the occurrence of large cracks while keeping manufacturing costs down and possessing sufficient wear resistance. [Solution] A contact material comprising a conductive substrate, a silver layer covering at least a portion of the surface of the conductive substrate, and a particle-containing metal layer covering at least a portion of the surface of the silver layer, wherein the silver layer has a thickness of 1.0 μm or more, and the particle-containing metal layer comprises a matrix made of a metal material and particles dispersed in the matrix.

Description

[Technical Field]

[0001] This disclosure relates to contact materials. [Background technology]

[0002] With the strengthening of CO2 emission regulations, an increase in electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs), which have a lower reliance on fossil fuels, is expected. Since these vehicles require daily battery charging, the contact terminal materials connecting the vehicle to the external power source must be designed to withstand a significantly greater number of insertions and removals compared to those used in conventional vehicles. Furthermore, high current flow is required to shorten the charging time. To minimize heat loss at the contacts, it is necessary to apply a surface treatment with low surface contact resistance to both the vehicle body side and the power source side contacts. In this field, highly conductive (low contact resistance) silver (Ag) plating is often used, but the hardness of Ag plating films is generally low, and "seizing" is likely to occur when Ag surfaces slide against each other, making wear a challenge when repeated insertions and removals (sliding) are performed.

[0003] Therefore, current electric vehicle charging terminals require a significantly thicker silver plating film (tens of micrometers thick) compared to the typical silver plating film (several micrometers thick) applied to contact materials, in order to prevent the base material from being exposed due to wear caused by repeated insertion and removal (sliding). This means an increase in the amount of silver required for the terminal components, leading to an increase in material costs. Furthermore, forming a thick silver plating film by electroplating requires a long electroplating process, which presents a challenge in terms of significantly reduced productivity.

[0004] To address these problems, a "particle-co-deposited Ag plating film," which incorporates particles of a non-conductive organic compound having an abrasion-inhibiting effect into the Ag plating layer, is known to be effective (for example, Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-154356 [Patent Document 2] Japanese Patent Publication No. 2024-006857 [Patent Document 3] Japanese Patent Publication No. 2020-128575 [Overview of the project] [Problems that the invention aims to solve]

[0006] When materials coated with a particle-co-deposited Ag plating film are subjected to processes such as bending or punching, cracks are more likely to occur in the plating film. This is mainly because the particle-plating interface within the particle-co-deposited Ag plating film is prone to becoming the starting point for crack formation. When cracks occur in the plating film applied to contact materials, although the adverse effects on the functionality of the contact material are minimal, there is a problem of deterioration in the visual appearance. In particular, if many large cracks occur, the appearance deteriorates significantly and will be avoided by users, so it is desirable to suppress the occurrence of large cracks.

[0007] Japanese Patent Publication No. 2020-128575 (Patent Document 3) discloses a connector terminal material (contact material) that can improve wear resistance, heat resistance, and crack resistance, comprising a silver layer coated on at least a portion of the surface of a substrate and a silver-platinum alloy layer coated on at least a portion of the silver layer. Wear resistance and heat resistance are improved by reacting the silver layer and the silver-platinum alloy layer to form an Ag3Pt intermetallic compound, and crack resistance is improved by thinning the film thickness of the Ag3Pt intermetallic compound to 0.04 μm or more and 1.9 μm or less. However, since platinum used in Patent Document 3 is expensive, there is a problem that the cost of the contact material increases.

[0008] This invention has been made in view of these circumstances, and one of its objectives is to provide a contact material that can suppress the occurrence of large cracks while keeping manufacturing costs down and having sufficient wear resistance.

Means for Solving the Problem

[0009] Aspect 1 of the present invention is a conductive substrate, a silver layer covering at least a part of the surface of the conductive substrate, and a particle-containing metal layer covering at least a part of the surface of the silver layer, and the silver layer has a thickness of 1.0 μm or more, the particle-containing metal layer is a contact material including a matrix phase made of a metal material and particles dispersed in the matrix phase.

[0010] Aspect 2 of the present invention is the contact material according to Aspect 1, wherein the silver layer has a silver content of 50 mass% or more and 100 mass% or less.

[0011] Aspect 3 of the present invention is the contact material according to Aspect 1 or 2, wherein the thickness of the silver layer with respect to the total thickness of the silver layer and the particle-containing metal layer is 10 to 60%.

[0012] Aspect 4 of the present invention is the contact material according to any one of Aspects 1 to 3, wherein the particles include non-conductive particles.

[0013] Aspect 5 of the present invention is the contact material according to Aspect 4, wherein the non-conductive particles are particles made of a non-conductive organic compound including any one or more selected from the group consisting of a fluoro group (-F), a methyl group (-CH3), a carbonyl group (-C(=O)-), an amino group (-NR 1 R 2 where R 1 and R 2 are hydrogen or a hydrocarbon group, and R 1 and R 2 may be the same or different), a hydroxy group (-OH), an ether bond (-O-), and an ester bond (-C(=O)-O-).

[0014] Aspect 6 of the present invention is The matrix phase is the contact material according to any one of Aspects 1 to 5, including one or more selected from the group consisting of silver and silver alloys.

[0015] Aspect 7 of the present invention is The contact material according to any one of Aspects 1 to 6, wherein the particle-containing metal layer satisfies the following formula (1). 2.0 ≦ A p / (A p + A Ag ) × 100 ≦ 12.0 ··· (1) In formula (1), A p is the area of the portion of the particles buried in the matrix phase in the cross-section in the thickness direction of the contact material, and A Ag is the area of the matrix phase in the cross-section in the thickness direction of the contact material.

[0016] According to an embodiment of the present invention, it is possible to provide a contact material that can suppress the generation of coarse cracks while suppressing the manufacturing cost and has sufficient wear resistance.

[0017] <00001Simplified Explanation of Drawings [Figure 1] [Figure 2] Figure 1 is a schematic cross-sectional view of an example of a contact material according to an embodiment of the present invention. [Figure 3A] Figure 2 is a schematic cross-sectional view of another example of a contact material according to an embodiment of the present invention. [Figure 3B] Figure 3A is a cross-sectional SEM image in the thickness direction of the contact material of the particle eutectic plating sample of Sample No. 9 in Example 2. [Figure 3C] Figure 3B is an image obtained by trimming only the particle-containing metal layer from Figure 3A. [Figure 4A] Figure 3C is an image obtained by binarizing Figure 3B. [Figure 4A] ​​Figure 4A is a graph showing the relationship between the coefficient of friction (□) and contact resistance (△) with respect to the particle eutectoid rate, obtained from the particle eutectoid plating sample No. 9 of Example 2. [Figure 4B] Figure 4B is a graph showing the relationship between the coefficient of friction (□) and contact resistance (△) with respect to the particle eutectoid rate, obtained from the particle eutectoid plating sample No. 10 of Example 2. [Figure 5A] Figure 5A is a cross-sectional SEM image of the contact material sample after the bending test. [Figure 5B] Figure 5B is a magnified view of the area enclosed by the dashed line in Figure 5A. [Figure 6A] Figure 6A is a cross-sectional SEM image of the contact material sample after the bending test. [Figure 6B] Figure 6B is a magnified view of the area enclosed by the dashed line in Figure 6A. [Figure 7] Figure 7 shows a cross-sectional SEM image of the contact material sample after the bending test. [Figure 8] Figure 8 shows a cross-sectional SEM image of the contact material sample after the bending test. [Modes for carrying out the invention]

[0018] Figures 1 and 2 are schematic cross-sectional views of the thickness direction of contact materials 1 and 11 according to embodiments of the present invention. The contact materials 1 and 11 include a conductive substrate 4, a silver layer 3 covering at least a portion of the surface 4a of the conductive substrate 4, and a particle-containing metal layer 2 covering at least a portion of the surface 3a of the silver layer 3. The particle-containing metal layer 2 includes a matrix 2a made of a metal material and particles 2b dispersed in the matrix 2a, while the silver layer 3 is substantially free of particles 2b.

[0019] The particle-containing metal layer 2 has higher wear resistance than a metal layer without particles 2b because particles 2b are dispersed in a matrix phase 2a made of a metal material. In other words, the contact materials 1 and 11 can have good wear resistance because they are equipped with the particle-containing metal layer 2. Furthermore, because the particle-containing metal layer 2 contains a matrix phase 2a made of a metal material, the particle-containing metal layer 2 as a whole is conductive regardless of what kind of particles 2b (for example, particles 2b made of conductive, non-conductive, inorganic, or organic materials) are dispersed in it.

[0020] The silver layer 3 is located between the conductive substrate 4 and the particle-containing metal layer 2. The silver layer 3 is a metal layer mainly composed of silver and has excellent malleability. Furthermore, the silver layer 3 substantially does not contain particles 2b. Therefore, it has the characteristic (crack resistance) that cracks are less likely to occur inside the silver layer 3, and even if cracks do occur, they are less likely to grow. Note that the silver layer 3 may contain a small amount of particles 2b, as long as it does not impair crack resistance. For example, if the content of particles 2b in the entire silver layer 3 (including particles 2b) is 1 volume percent or less, wear resistance can be slightly improved without substantially worsening crack resistance.

[0021] When tensile stress is applied to the particle-containing metal layer 2 due to processing of contact materials 1 and 11, cracks may occur in the particle-containing metal layer 2, starting from the particles 2b dispersed within the particle-containing metal layer 2. These cracks grow further due to the tensile stress. Crack growth refers to an increase in crack width and extension in the depth direction. When observed from the surface side of the particle-containing metal layer 2, the grown cracks appear as wide cracks (referred to as "coarse cracks"), and when observed in the thickness-direction cross-section of contact materials 1 and 11, the cracks appear as wide cracks on the surface side of the particle-containing metal layer 2, extending long in the direction of the conductive substrate 4 (depth direction).

[0022] If a crack that originates in the particle-containing metal layer 2 continues to grow, it will attempt to cross the silver layer 3 and reach the conductive substrate 4. However, because the silver layer 3 is crack-resistant, it can stop cracks that extend in the depth direction. When the extension of the crack in the depth direction stops (i.e., the crack growth stops), the widening of the crack also stops. In this way, by providing the silver layer 3 between the conductive substrate 4 and the particle-containing metal layer 2, the growth of cracks that originate in the particle-containing metal layer 2 can be stopped, thereby suppressing the occurrence of large cracks in the particle-containing metal layer 2.

[0023] Thus, in the contact materials 1 and 11 according to this embodiment, by laminating the silver layer 3 and the particle-containing metal layer 2 in this order on the surface of the conductive substrate 4, the wear resistance can be improved by the particle-containing metal layer 2 present on the surface side of the contact materials 1 and 11, and the silver layer 3 located between the particle-containing metal layer 2 and the conductive substrate 4 can suppress the occurrence of coarse cracks in the particle-containing metal layer 2. Unlike reference document 3, the contact materials 1 and 11 according to this embodiment do not require the use of platinum, and therefore manufacturing costs can be reduced.

[0024] Furthermore, while Reference 3 also discloses the provision of a silver layer between the substrate and the silver-platinum alloy layer, this silver layer is provided as a silver source for forming the Ag3Pt intermetallic compound and is not intended to suppress cracking.

[0025] The silver layer 3 of the contact materials 1 and 11 according to this embodiment is formed from a metallic material mainly composed of silver, such as pure silver or a silver alloy. That is, the silver content in the silver layer 3 is 50% by mass or more and 100% by mass or less, preferably 90% by mass or more and 100% by mass or less, and more preferably 99% by mass or more and 100% by mass or less. By increasing the silver content in the silver layer 3, a silver layer 3 with better ductility (i.e., better crack resistance) can be formed, thereby more effectively suppressing the occurrence of coarse cracks in the particle-containing metal layer 2.

[0026] The ratio of the thickness of the silver layer 3 (3t) to the thickness of the particle-containing metal layer 2 (2t) can affect the wear resistance of the contact materials 1 and 11, as well as the effect of suppressing the occurrence of coarse cracks. Therefore, it is preferable to control the thickness ratio to an appropriate level. In particular, the ratio of the thickness of the silver layer 3 (3t) to the total thickness of the silver layer 3 and the particle-containing metal layer 2 (3t + 2t) (referred to as the "thickness ratio of silver layer 3") is preferably 10 to 60%. A thickness ratio of silver layer 3 of 10% or more can more effectively suppress the occurrence of coarse cracks in the particle-containing metal layer 2. A thickness ratio of silver layer 3 of 60% or less can ensure a sufficient thickness of the particle-containing metal layer 2 (2t), thereby further improving the wear resistance of the contact materials 1 and 11. The thickness ratio of the silver layer 3 is more preferably 15% or more, even more preferably 20% or more, preferably 50% or less, more preferably 45% or less, even more preferably 40% or less, and particularly preferably 30% or less.

[0027] The specific thickness 3t of the silver layer 3 is preferably determined by balancing it with the particle-containing metal layer 2 formed on the contact materials 1 and 11, but it should be at least 1.0 μm or more, for example, it may be greater than 1.0 μm and less than or equal to 10 μm, preferably 1.2 μm or more, more preferably 1.5 μm or more, preferably 5.0 μm or less, and more preferably 3.0 μm or less. Within this thickness range, it is possible to provide sufficient crack resistance to the contact materials 1 and 11 while keeping the manufacturing cost of the contact materials 1 and 11 down. The thickness 2t of the particle-containing metal layer 2 is not particularly limited and can be adjusted as appropriate depending on the application, but for example, it may be 100 μm or less, or even 50 μm or less.

[0028] The thickness of the silver layer 3 (3t) and the thickness of the particle-containing metal layer 2 (2t) can be quantified from cross-sectional SEM images of samples of the contact materials 1 and 11, cut in the thickness direction of the contact materials 1 and 11 (substantially coinciding with the direction perpendicular to the surface of the conductive substrate 4). The cross-sectional SEM images are taken at a magnification of 1000x, so that the vertical direction of the observation field coincides with the thickness direction of the contact materials 1 and 11. The field of view is, for example, 140 μm vertically × 200 μm horizontally.

[0029] In measuring the thickness of the silver layer 3 (3t), the boundary between the silver layer 3 and the conductive substrate 4 (referred to as the "first boundary," which basically coincides with the surface 4a of the conductive substrate 4) and the boundary between the silver layer 3 and the particle-containing metal layer 2 (referred to as the "second boundary," which basically coincides with the surface 3a of the silver layer 3) are first identified in a cross-sectional SEM image. The distance between the first boundary and the second boundary in a direction perpendicular to the surface 4a of the conductive substrate 4 is measured and defined as the "thickness of the silver layer 3 (3t)."

[0030] The thickness 2t of the particle-containing metal layer 2 varies depending on the state of the particles 2b dispersed in the particle-containing metal layer 2. As will be described in detail later, the particle-containing metal layer 2 can take two forms: one in which some of the particles 2b protrude outward from the surface 2c of the matrix phase 2a, as shown in Figure 1, and another in which all of the particles 2b are completely embedded in the matrix phase 2a, as shown in Figure 2.

[0031] In the case of a particle-containing metal layer 2 having the morphology shown in Figure 1, the distance between the second boundary (surface 3a of the silver layer 3) and the top of the protruding particle 2b is defined as the "thickness 2t of the particle-containing metal layer 2". In the cross-sectional SEM image, the second boundary and the particle 2b that protrudes most from the surface 2c of the matrix 2a are identified. The distance between the second boundary and the top of the most protruding particle 2b in a direction perpendicular to the surface 4a of the conductive substrate 4 is measured and defined as the "thickness 2t of the particle-containing metal layer 2". Furthermore, in areas where no protruding particles 2b exist, that is, in areas where the surface 2c of the matrix phase 2a is exposed, the "thickness 2at of the matrix phase 2a" can be measured. The distance between the second boundary and the surface 2c of the matrix phase 2a in a direction perpendicular to the surface 4a of the conductive substrate 4 is the "thickness 2at of the matrix phase 2a".

[0032] In the case of a particle-containing metal layer 2 having the form shown in Figure 2, the distance between the second boundary (surface 3a of the silver layer 3) and the surface 2c of the matrix 2a is defined as the "thickness 2t of the particle-containing metal layer 2". The second boundary and the surface 2c of the matrix 2a are identified in the cross-sectional SEM image. The distance between the second boundary and the surface 2c of the matrix 2a in the direction perpendicular to the surface 4a of the conductive substrate 4 is measured and defined as the "thickness 2t of the particle-containing metal layer 2". In the particle-containing metal layer 2 shown in Figure 2, the thickness 2at of the matrix phase 2a is equal to the thickness 2t of the particle-containing metal layer 2.

[0033] The thickness of each layer may be measured once at any position within the field of view of the SEM image, or it may be measured at any 2 to 5 locations and the arithmetic mean of the obtained measurement results may be used. However, in the case of a particle-containing metal layer 2 with the morphology shown in Figure 1, the "thickness 2t of the particle-containing metal layer 2" is measured at the position where the particle 2b protrudes the most, as explained above.

[0034] The silver layer 3 and the particle-containing metal layer 2 can be distinguished by the method described below.

[0035] The conductive substrate 4 can be formed from a plate, foil, wire, or rod made of a metal such as copper or a copper alloy. The thickness 4t of the conductive substrate 4 is, for example, 1 μm to 100 mm.

[0036] As described above, the particle-containing metal layer 2 comprises a matrix phase 2a made of a metallic material and particles 2b dispersed in the matrix phase 2a. There are two main dispersion states of particles 2b in the matrix phase 2a (Figures 1 and 2).

[0037] In the contact material 1 shown in Figure 1, many particles 2b are completely embedded in the matrix 2a. However, particles 2b located near the surface 2c of the matrix 2a partially protrude outward from the surface 2c of the matrix 2a. In other words, near the surface 2c of the matrix 2a, there are particles 2b that are partially embedded in the matrix 2a and the remaining parts exposed from the surface 2c of the matrix 2a. If the wear resistance of the contact material 1 is to be improved by the decomposition of particles 2b, it is preferable that the particles 2b are partially exposed from the surface 2c of the matrix 2a, as shown in Figure 1. From the initial stages of use of the contact material 1, the particles 2b can be decomposed by the insertion and removal (sliding) of the contact material 1, thereby improving wear resistance.

[0038] In the contact material 11 shown in Figure 2, all particles 2b are completely embedded in the matrix phase 2a. In other words, even when observing from the surface side of the particle-containing metal layer 2, the particles 2b cannot be directly observed. If the particles 2b are formed from a non-conductive material, the electrical conductivity of the particle-containing metal layer 2 can be improved (contact resistance can be further reduced) by preventing the particles 2b from being exposed from the surface 2c of the matrix phase 2a, as shown in Figure 2. In addition, wear resistance can be improved as the matrix phase 2a is worn down by the insertion and removal (sliding) of the contact material 1, and the embedded particles 2b are exposed.

[0039] The metal material forming the matrix 2a preferably includes one or more selected from the group consisting of silver and silver alloys. In particular, the matrix 2a preferably contains silver in a range of 50% to 100% by mass. In addition to various silver platings used in ordinary terminal surface treatments (e.g., soft Ag plating, hard Ag plating, bright Ag plating, and semi-bright Ag plating), silver alloy plating may also be used as the matrix 2a for the purpose of improving the corrosion resistance (sulfidation resistance, etc.) and wear resistance of the matrix 2a. Examples of silver alloys suitable for silver alloy plating include Ag-Sn, Ag-Sb, and Ag-Cu.

[0040] Furthermore, by using pure silver plating for the matrix 2a, a particle-containing metal layer 2 with excellent conductivity can be obtained. The matrix 2a may contain silver in a range of 90% to 100% by mass, 95% to 100% by mass, or 99% to 100% by mass.

[0041] Furthermore, the silver material forming the silver layer 3 and the metal material forming the matrix 2a may be the same or different. When the silver layer 3 and the matrix 2a are formed from different metallic materials, the types or amounts of alloying elements contained in the silver layer 3 and the matrix 2a differ. Therefore, the silver layer 3 and the matrix 2a can be distinguished by elemental mapping using cross-sectional SEM-EDX analysis. In other words, cross-sectional SEM-EDX analysis can distinguish between the extent of the silver layer 3 and the extent of the particle-containing metal layer 2, which includes the matrix 2a.

[0042] When the silver layer 3 and the matrix 2a are formed from the same metallic material, it is not possible to distinguish between the silver layer 3 and the matrix 2a by cross-sectional SEM-EDX analysis. Therefore, it is necessary to distinguish between the extent of the silver layer 3 and the extent of the matrix 2a (particle-containing metal layer 2) by another method. In this case, the region containing particles 2b is designated as "particle-containing metal layer 2," and the region not containing particles 2b is designated as "silver layer 3." As mentioned above, the silver layer 3 may contain trace amounts of particles 2b, but when the silver layer 3 and the matrix 2a are formed from the same metallic material, the silver layer 3 is assumed not to contain particles 2b in order to facilitate the identification of the first boundary.

[0043] The boundary between the silver layer 3 and the particle-containing metal layer 2 (the second boundary) is identified by a cross-sectional SEM image of the contact materials 1 and 11 in the thickness direction. The cross-sectional SEM image is processed using a method described later to identify all particles 2b contained in the particle-containing metal layer 2. Based on the particle 2b closest to the conductive substrate 4, the boundary between the silver layer 3 and the conductive substrate 4 (the second boundary) is determined. In other words, the second boundary is drawn such that, on the cross-sectional SEM image, the particle 2b closest to the conductive substrate 4 is located on the particle-containing metal layer 2 side of the second boundary, and that this particle 2b is in contact with the second boundary. The second boundary on the cross-sectional SEM image is straight and drawn approximately parallel to the surface of the conductive substrate 4.

[0044] Various types of particles can be used as particle 2b, but non-conductive particles are particularly preferred. When the particle-containing metal layer 2 is applied to the contact material and subjected to repeated sliding (insertion and removal), the particles 2b held in the matrix phase 2a may fall off as the particle-containing metal layer 2 wears down. If the particles 2b are non-conductive particles, it is advantageous because even if the particles 2b fall off and accumulate near the contact, the possibility of a short circuit occurring is low. Here, "non-conductive" means that it does not exhibit conductivity, for example, the volume resistivity measured according to ASTM D257 is approximately 10. 3 This refers to values ​​greater than or equal to [Ω·cm].

[0045] Non-conductive particles have a fluoro group (-F), a methyl group (-CH3), a carbonyl group (-C(=O)-), and an amino group (-NR) within their unit molecular structure. 1 R 2 And R 1 and R 2 R is a hydrogen or hydrocarbon group, 1 and R 2 Preferably, the particles are made of a non-conductive organic compound containing one or more selected from the group consisting of a hydroxyl group (-OH), an ether bond (-O-), and an ester bond (-C(=O)-O-).

[0046] Here, "organic compound" refers to a compound containing carbon, excluding compounds with simple structures such as carbon monoxide, carbon dioxide, carbonates, hydrogen cyanide, cyanates, thiocyanates, B4C, and SiC. For example, a silicone resin with a siloxane bond (-Si-O-Si-) as its main chain and organic groups in its side chains is included in the definition of "organic compound" as defined herein.

[0047] The nonconductive organic compound forming particle 2b contains the functional groups described above, thereby improving the wear resistance of the particle-containing metal layer 2. Here, "unit molecular structure" refers to one repeating unit in the case of a polymer, and to individual molecules in the case of a nonpolymer.

[0048] The reason why using particles made of non-conductive organic compounds can improve the wear resistance of the particle-containing metal layer 2 is not clear, but the following mechanism is hypothesized. It is believed that when the particle-containing metal layer 2 slides, for example, some of the non-conductive organic compound decomposes and diffuses to the vicinity of the contact material surface, and / or some of the non-conductive organic compound reacts with the silver-containing layer near the contact material surface, thereby lowering the coefficient of friction near the contact material surface and improving the wear resistance of the contact material. It is thought that the non-conductive organic compound has a particularly strong effect in promoting the decomposition of the compound due to sliding because it has a predetermined functional group in its unit molecular structure. Furthermore, since the amount of decomposition products and reactants is small, and the proportion of particles consisting of the specific non-conductive organic compound in the silver-containing film is controlled to be below a predetermined value, it is believed that sufficient conductivity can be ensured.

[0049] The particle size of particle 2b is preferably such that it can be dispersed within the matrix phase 2a of the particle-containing metal layer 2 and does not hinder the conductivity of the particle-containing metal layer 2. For example, the particle size (equivalent diameter) of particle 2b is less than the thickness 2at of the matrix phase 2a. This suppresses situations in which particle 2b protrudes significantly from the surface 2c of the matrix phase 2a and hinders conductivity between the particle-containing metal layer 2 and the external terminal. Furthermore, it is more preferable that the equivalent diameter of particle 2b is sufficiently smaller than the thickness 2at of the matrix phase 2a (for example, less than or equal to half the thickness 2at of the matrix phase 2a), so that particle 2b can be completely embedded in the matrix phase 2a (however, this does not mean that all particle 2b is completely embedded, but rather that there may be particles 2b that are completely embedded in the matrix phase 2a). The average particle size (average circle equivalent diameter) of particle 2b may be, for example, 50 μm or less, 10 μm or less, or 0.1 μm or more. The method for measuring the thickness 2at of the matrix phase 2a is as described above.

[0050] The area of ​​particles 2b (mainly non-conductive particles) and matrix 2a in the particle-containing metal layer 2, as confirmed by a cross-sectional SEM image, preferably satisfies the following equation (1). 2.0 ≤ A p / ( A p +A Ag ) × 100 ≤ 12.0 ···(1) In equation (1), A p This is the area of ​​the portion of the particles embedded in the matrix 2 in the cross-section in the thickness direction of the contact materials 1 and 11, and A Ag This represents the area of ​​the matrix 2 in the cross-section in the thickness direction of the contact materials 1 and 11.

[0051] Equation (1) means that the area ratio of particles contained within the particle-containing metal layer 2 is 2.0% to 12.0% of the total area ratio of the particle-containing metal layer 2. Since the particle-containing metal layer 2 containing particles 2b can be formed by the co-deposition plating method (a method of electroplating by placing particles in a plating solution and stirring), the area ratio of the contained particles is sometimes referred to as the "particle co-deposition ratio".

[0052] The particles contained in the particle-containing metal layer 2 contribute to the wear resistance of the particle-containing metal layer 2, but reduce its conductivity. When the area ratio (volume ratio) of the particles is 2.0% or more, the wear resistance of the particle-containing metal layer 2 can be significantly improved, while when it is 12.0% or less, the reduction in conductivity of the particle-containing metal layer 2 can be kept to a minimum. In other words, when the area ratio (volume ratio) of the particles is between 2.0% and 12.0%, both the wear resistance and conductivity of the particle-containing metal layer 2 can be achieved at a high level. The area ratio (particle eutectoid ratio) of the particles is more preferably 6.0% or more, and more preferably 10.0% or less.

[0053] Area A of matrix 2a Ag This can be determined by binarizing the cross-sectional SEM image of the thickness-direction cross-section of the contact materials 1 and 11 using image processing software (e.g., "ImageJ"). Specifically, in the cross-sectional SEM image, the matrix 2a may appear relatively bright (i.e., white), and the protective layer of the sample for cross-sectional SEM may appear relatively dark (i.e., black). For example, the area of ​​the bright part after binarization using the brightness intermediate between the matrix 2a and the protective layer as a threshold is the area A of the matrix 2a. Ag This can be done. Furthermore, if there are irregularities on the upper surface of the silver-containing layer 2a in the cross-sectional SEM image, the area of ​​the matrix 2a may be determined by using the average line of these irregularities as the boundary line between the matrix 2a and the upper layer (for example, the protective layer of the sample for cross-sectional SEM).

[0054] On the other hand, the area A of the portion of particle 2b that is embedded in the matrix 2a. p This can be the area of ​​the dark portion after binarization (in the case of non-conductive particles, the portion corresponding to the non-conductive organic compound) that is embedded in the matrix 2a. In the cross-sectional SEM image, if there are irregularities on the surface 2c of the matrix 2a, the average line of these irregularities is used as the boundary line between the matrix 2a and the upper layer (for example, the protective layer of the sample for cross-sectional SEM), and the portion below this average line is considered to be the portion embedded in the matrix 2a.

[0055] Without departing from the objective of the embodiments of the present invention, the contact materials 1 and 11 may contain particles other than nonconductive particles 2b. For example, the contact materials 1 and 11 may contain particles made of nonconductive organic compounds that do not contain the specific functional groups described above, or they may contain inorganic particles, or they may contain particles that are not embedded in the matrix 2a. The contact materials 1 and 11 may also contain conductive particles, but the less conductive particles there are, the more preferable it is to suppress short circuits at the contacts due to the shedding of conductive particles. For example, it is preferable that 50 volume% or more of the particles contained in the contact materials 1 and 11 are nonconductive particles 2b, more preferably 60 volume% or more, 70 volume% or more, 80 volume% or more, or 90 volume% or more, and even more preferably all (100 volume%) are nonconductive particles 2b. Furthermore, the ratio of particles 2b, at least partially embedded in the matrix 2a, to all particles contained in the contact materials 1 and 11 is preferably 50 area % or more, more preferably 60 area % or more, 70 area % or more, 80 area % or more, 90 area % or more, and even more preferably 100 area %.

[0056] The contact materials 1 and 11 according to the embodiment of the present invention may include other layers (e.g., a conductive substrate, a strike plating layer, etc.) in order to achieve the objectives of the present invention. For example, in the contact materials 1 and 11, a silver-containing film 2 may be formed on a conductive substrate (e.g., a substrate made of copper or a copper alloy).

[0057] In the embodiment of the present invention, contact materials 1 and 11 are obtained by, for example, forming a silver layer 3 on a substrate, then dispersing a predetermined amount of particles 2b in a silver (or silver alloy) plating solution, and performing a silver plating treatment by applying an electric current while stirring, thereby obtaining a contact material in which a predetermined amount of particles 2b are embedded (co-deposited) in the matrix phase 2a.

[0058] In the process of electroplating by dispersing particle 2b in a plating solution, the following reactions (A) and (B) proceed simultaneously. (A) A reaction in which liquid-dispersed particles are electrostatically or physically adsorbed (in contact) onto the surface of the substrate. (B) A reaction in which matrix phase 2a is deposited (grown) on the surface of the substrate. "Eutectoid formation" occurs when particles 2b adsorbed in (A) are incorporated into the matrix phase 2a in (B). Under conditions where eutectoid plating proceeds steadily, the particles 2b adsorbed in the initial stages of the reaction are incorporated into the matrix phase 2a, and at the same time, new particles 2b are adsorbed. For this reason, even when the plating process is stopped, in most cases, exposed particles 2b can be seen on the outermost surface, and in a normal eutectoid plating process, contact material 1 (see Figure 1) containing particles 2b, some of which are embedded in the matrix phase 2a and the rest of which are exposed on the surface of the matrix phase 2a can be easily manufactured.

[0059] Here, the amount of particles 2b co-deposited into the matrix phase 2a (for example, the area ratio of particles 2b) is determined by the balance between the adsorption frequency of (A) and the plating film growth rate of (B). Therefore, it is possible to change the amount of co-deposited particles by changing the plating conditions, such as the amount of particles 2b dispersed in the plating solution. For example, by performing the plating process using a plating solution that does not contain dispersed particles 2b at the end of the plating process, or by changing the stirring speed of the plating solution to reduce the adsorption frequency of (A), it is possible to create a layer on the outermost surface of the plating in which particles 2b do not co-deposit, thereby producing a contact material 11 (see Figure 1) in which all particles 2b are embedded in the matrix phase 2a. [Examples]

[0060] The embodiments of the present invention will be described in more detail below with reference to examples. The embodiments of the present invention are not limited by the following examples, and can be implemented with appropriate modifications within the scope that is consistent with the spirit described above and below, and all such modifications are included within the technical scope of the embodiments of the present invention. [Examples]

[0061] <Method for creating particle-coated plating> To easily identify the molecular structure conditions of particles that provide excellent wear resistance, the wear resistance and conductivity of Ag plating coated with these particles were evaluated. A 0.3mm thick pure copper plate was used as the plating substrate. After degreasing the surface with acetone cleaning, a commercially available Strike Ag plating solution (Dyne Silver GPE-ST, manufactured by Yamato Kasei Co., Ltd.) was used as the base for the plating process, with a Pt-coated Ti plate as the counter electrode at 5 A / dm². 2 A current density of approximately 0.1 μm was applied for 1 minute, and a strike Ag plating treatment was performed on the substrate. Subsequently, a commercially available non-cyanide semi-bright Ag plating solution (Dain Silver GPE-SB, Yamato Kasei Co., Ltd.) was used, with a pure Ag plate as the counter electrode, and a current density of 3 A / dm was applied. 2 A current density was applied for 5 minutes to form a semi-gloss Ag plating layer with a thickness of approximately 10 μm. Samples for evaluating wear resistance were prepared by dropping a solution containing the particles shown in Tables 1 and 2 suspended in alcohol onto the surface of a plated sample and allowing it to dry. Note that sample No. 1 was not coated with the alcohol suspension of particles.

[0062] <Method for evaluating wear resistance> A sample was prepared by forming a hard Ag plating (Vickers hardness HV: approximately 165) layer of approximately 50 μm on a 0.25 mm thick pure copper plate, and then creating an embossed shape with R=1.8 mm by hand pressing. This sample was used as a mating material, and a friction sliding test was conducted for a maximum of 500 cycles between it and a sample for wear resistance evaluation (using a horizontal load testing machine manufactured by Aiko Engineering). The applied vertical load was 3 N, the sliding distance was 10 mm, and the sliding speed was 80 mm / min. The maximum value of the friction coefficient (ratio of horizontal load to vertical load) was measured in each sliding cycle, and the friction coefficient μ was read after 100, 300, and 500 cycles, respectively. Those with μ ≤ 0.50 at 100 cycles were classified as "Excellent" for their particularly superior friction improvement effect, those with μ ≤ 0.50 at 300 cycles were classified as "Good", and those with μ > 0.50 even at 500 cycles were classified as "Unacceptable". "Excellent" and "Good" were considered passing grades.

[0063] <Contact Resistance Test Method> The contact resistance at the contact points was measured using a micro-sliding abrasion tester manufactured by Yamazaki Seiki Kenkyusho, targeting wear marks after friction testing. The applied load was 5N, and the average value of measurements taken at three points was used as the contact resistance for evaluation. Samples with a contact resistance of 0.500 mΩ or less after friction testing were judged to have "excellent contact resistance" and were deemed to pass. Contact resistance measurements were not performed on samples that failed abrasion resistance testing.

[0064] The results above are summarized in Table 2.

[0065] [Table 1]

[0066] [Table 2]

[0067] Samples No. 2 to 8, which satisfy the requirements of the embodiments of the present invention, were found to maintain a low coefficient of friction after 300 and 500 cycles of friction testing, and their contact resistance after the friction testing was also confirmed to be good. In sample No. 1, the evaluated material was a simple Ag plating layer and lacked the particle-containing metal layer 2. As a result, it easily seized up with the mating material and exhibited poor wear resistance. [Examples]

[0068] <Method for preparing particle co-deposition plating samples> To confirm the effect of particle-containing metal layer 2, a sample (particle-co-deposited plating sample) was prepared with a particle-co-deposited plating layer in which particles were actually co-deposited into the Ag plating layer. The wear resistance and conductivity were evaluated by varying the particle co-deposition rate of the particle-co-deposited plating. In the process of forming a 10 μm thick Ag plating layer on a strike-plated copper substrate as described in Example 1, a predetermined amount of particles were dispersed in the plating solution, and electroplating was performed while stirring to obtain a plating layer in which each particle was incorporated (co-deposited) into the Ag plating layer. In some cases, the use of a surfactant (dispersant) was necessary to prevent the aggregation of each particle in the Ag plating layer and to maintain a stable dispersion state. The obtained particle co-deposition plated samples were subjected to friction tests and contact resistance measurements and evaluations using the same method as in Example 1.

[0069] <Method for calculating particle deposition rate by observing the plated cross-section> The particle co-deposition rate of the obtained particle co-deposition plated sample was determined by the following formula. Using a scanning electron microscope (SEM, Hitachi S-3500N), under conditions of an acceleration voltage of 20kV and a work distance of 15mm, cross-sectional SEM images (secondary electron images) were obtained of particle eutectoid plated samples No. 10-11, which were coated with a protective layer for cross-sectional SEM, in the thickness direction of contact materials 1 and 11. Area A of matrix 2 Ag Area A was defined as the area of ​​the bright portion after the cross-sectional SEM image was binarized using the image processing software "ImageJ" as described above. In the cross-sectional SEM image, the average line of the irregularities on the upper surface of matrix 2 was used as the boundary line between matrix 2 and the protective layer of the sample for cross-sectional SEM. Area A represents the portion of multiple particles embedded in the silver-containing layer. p This refers to the area of ​​the dark portion (corresponding to the non-conductive organic compound) after the binarization process described above, which is the area of ​​the portion embedded in the matrix 2. In the cross-sectional SEM image, the average line of the irregularities on the upper surface of the matrix 2 was used as the boundary line between the particle-containing metal layer 2 and the protective layer of the cross-sectional SEM sample, and the portion below this average line was considered to be the portion embedded in the matrix 2.

[0070] Figures 3A to 3C show examples of calculating the particle area ratio (particle co-deposition ratio). Figure 3A is a cross-sectional SEM image in the thickness direction of a particle co-deposition plated sample prepared with a particle dispersion amount of 3 g / L in liquid for sample No. 9. Figure 3B is an image cropped from Figure 3A showing only matrix 2 (and particles embedded in matrix 2). Figure 3C is a binarized image of Figure 3B. When the area of ​​the black part in Figure 3C was divided by the area in Figure 3B, the area ratio (particle co-deposition ratio) was 2.51%.

[0071] Based on these analysis results, the range of particle co-deposition ratios that can achieve both wear resistance and conductivity was determined from the perspective of friction coefficient and contact resistance (Figures 4A and 4B). Here, a particle co-deposition ratio that satisfies "friction coefficient of 0.50 or less and contact resistance of 0.500 mΩ or less" was judged as acceptable. The measurement results are shown in Table 3.

[0072] [Table 3]

[0073] Sample No. 9 is a sample equipped with cross-linked polymethyl methacrylate particle eutectoid plating. Figure 4A shows the relationship between the coefficient of friction and contact resistance with respect to the particle eutectoid rate for sample No. 9. In particle eutectoid plating with a particle eutectoid rate of 2.0% to 12.0%, the coefficient of friction stabilized at approximately 0.4 after 20 sliding cycles, and the contact resistance remained below 0.500 mΩ, confirming that good wear resistance and conductivity were achieved simultaneously.

[0074] Sample No. 10 is a sample equipped with polyethylene oxide particle eutectoid plating. Figure 4B shows the relationship between the coefficient of friction and contact resistance with respect to the particle eutectoid rate for sample No. 10. In the particle eutectoid plating with a particle eutectoid rate of 0.5%, the coefficient of friction decreased to about 0.2 after 20 sliding cycles, and further stabilized at about 0.1 when the particle eutectoid rate was 2.0% or higher. The contact resistance remained almost unchanged in the range of particle eutectoid rates from 0% to 8.0%, maintaining approximately 0.3 mΩ. It was confirmed that good wear resistance and conductivity could be achieved simultaneously when the particle eutectoid rate was 0.5% or higher.

[0075] The range of particle co-deposition ratios that allows for both a low coefficient of friction and low contact resistance varies depending on the type of particle. [Examples]

[0076] <Method for creating a two-layer plating structure for bending tests> After degreasing the surface of a 0.3mm thick pure copper plate with alkaline cleaning, a nickel sulfamate plating solution was used as a base treatment to prevent copper diffusion from the pure copper plate, at 5 A / dm 2 A current density was applied for 90 seconds to form a Ni plating layer approximately 1 μm thick. Next, as a surface treatment to prevent the Ag substitution reaction, a commercially available Strike Ag plating solution (Dyne Silver GPE-ST, manufactured by Yamato Kasei Co., Ltd.) was used, with an iridium oxide coated Ti plate as the counter electrode at 3 A / dm². 2 The substrate was subjected to a strike Ag plating treatment with a thickness of approximately 0.1 μm or less by applying current at the specified current density for 10 seconds, and then used as a base material.

[0077] For the above substrate, a commercially available non-cyanide semi-bright Ag plating solution (Dyne Silver GPE-SB, manufactured by Yamato Kasei Co., Ltd.) was used as the silver layer 3, with a pure Ag plate as the counter electrode at 3 A / dm². 2 A current density of approximately 5 μm was applied for 270 seconds to form an Ag plating layer.

[0078] Next, as the particle-containing metal layer 2, a commercially available non-cyanide semi-bright Ag plating solution (Dyne Silver GPE-SB, manufactured by Yamato Kasei Co., Ltd.) was used. After adding a surfactant (Surflon S231, manufactured by AGC Seimi Chemical) to the solution, the particles shown in Table 4 were added, and while stirring, a pure Ag plate was used as the counter electrode at 3 A / dm². 2 A current density was applied for 270 seconds to form a particle-co-deposited Ag plating layer with a thickness of approximately 5 μm. The ratio of the thickness of silver layer 3 to the total thickness of silver layer 3 and particle-containing metal layer 2 was 50%.

[0079] These procedures yielded contact material samples (samples No. 11 and 12) comprising a silver layer 3 (pure Ag) and a particle-containing metal layer 2 in which particles were co-deposited (embedded). For comparison, we also prepared two contact material samples: one with only the particle-containing metal layer 2 formed (i.e., without the silver layer 3) (Sample No. 13), and another with only the silver layer 3 formed (i.e., without the particle-containing metal layer 2) (Sample No. 14).

[0080] [Table 4]

[0081] <Method for evaluating bendability> The obtained contact material samples (samples No. 11-14) were cut into 10 mm wide strips and subjected to bending tests. The bending tests were performed using a W-bending test jig conforming to JIS H 3110. A radius of R=0.5 mm was used. To confirm the crack formation in the cross-section of the bent portion of the sample, the cross-section of the 90° bend apex during the bending test was observed. A scanning electron microscope (SEM: BRUKER - Hitachi, QUANTAX) was used to acquire cross-sectional SEM images (secondary electron images) under the conditions of 1000x magnification, 20kV acceleration voltage, and a work distance of 15mm. The field of view was set to 140μm vertically × 200μm horizontally, and the silver layer 3 and particle-containing metal layer 2 at the 90° bend apex were observed.

[0082] In the obtained cross-sectional SEM images, those satisfying the following conditions A to D were identified as cracks. In the cross-sectional SEM images, the silver layer 3 and the matrix 2a of the particle-containing metal layer 2 were observed as white or light gray areas, while the particles 2b of the particle-containing metal layer 2, cracks, and the embedded resin (used when preparing the sample for cross-sectional observation) were observed as dark gray areas.

[0083] A. This is a dark gray area located inside the surface line of the particle-containing metal layer 2 (towards the conductive substrate 4), and is exposed from the surface of the particle-containing metal layer 2. B. Area is 2π (μm 2That's all. C. The entire crack is visible within the field of view. D. The dimension perpendicular to the surface 4a of the conductive substrate 4 (crack length) is 2 μm or more. If the surface 4a of the conductive substrate 4 is curved, the tangent line at a point on the surface 4a that is intended to define the perpendicular direction is defined as "surface 4a" to specify the perpendicular direction.

[0084] Condition A is a condition for eliminating the embedding resin covering the particle-containing metal layer 2 and internal defects (defects not exposed on the surface) in the particle-containing metal layer 2. This is because cracks observed from the surface in a plan view of the particle-containing metal layer 2 degrade the appearance. Condition B is a condition for excluding particle 2b. Since particle 2b has a D50 of 2 μm, its area in the cross-sectional SEM image is π μm. 2 It is estimated that this will be observed as a dark gray particulate region of approximately 2π(μm²). Considering the variation in particle size of particle 2b, the area is twice the estimated area, which is 2π(μm²). 2 Dark gray areas less than ) are considered "particle 2b" and are not cracks. Condition D is intended to eliminate minute irregularities on the surface of the particle-containing metal layer 2.

[0085] Once the crack is identified, the crack width is measured at various locations along the crack, and the largest value (the maximum crack width) is determined. Here, "crack width" refers to the dimension of the crack measured in a direction parallel to the surface 4a of the conductive substrate 4 on the cross-sectional SEM image. If the surface 4a of the conductive substrate 4 is not flat and the direction for measuring the crack width cannot be uniquely determined on the cross-sectional SEM image, the measurement direction was determined based on the contact points between the inner surface of the crack and the surface 4a of the conductive substrate 4. Since the inner surface of the crack is composed of two opposing surfaces, there are two contact points between the inner surface of the crack and the surface 4a of the conductive substrate 4. The direction parallel to the line connecting these contact points was used as the direction for measuring the crack width.

[0086] Samples with a maximum crack width of 10 μm or more were judged as defective, those with a maximum crack width of less than 10 μm were judged as good, and those with no cracks were judged as excellent. If the judgment was good or excellent, the bendability was judged as "pass," and if the judgment was poor, the bendability was judged as "fail."

[0087] Figure 5A shows a cross-sectional SEM image of the 90° bend apex of the contact material sample No. 11 from Table 3 after a bending test, and it can be seen that a crack has occurred. As shown in Figure 5B, the maximum width of the crack was 4.4 μm (good), and the bendability was "acceptable". Figure 6A shows a cross-sectional SEM image of the 90° bend apex of the contact material sample No. 12 from Table 3 after a bending test, and it can be seen that a crack has occurred. As shown in Figure 6B, the maximum width of the crack was 1.5 μm (good), and the bendability was "acceptable". Figure 7 shows a cross-sectional SEM image of the 90° bend apex of the contact material sample No. 13 from Table 3 after a bending test, revealing the presence of cracks. Because silver layer 3 was not formed, the maximum crack width was 19.2 μm (poor), and the bendability was "failed". Figure 8 shows a cross-sectional SEM image of the 90° bend apex of the contact material sample No. 14 from Table 3 after a bending test. Since it does not contain particle-containing metal layer 2, no cracks occurred (bendability rating: excellent). [Explanation of Symbols]

[0088] 1, 11 Contact material 2 Particle-containing metal layer 2a Matrix 2b particles (non-conductive particles) 2c Surface of matrix 3 silver layer 3a Surface of the silver layer 4 Conductive base material 4a Surface of conductive substrate

Claims

1. A conductive substrate and A silver layer covering at least a portion of the surface of the conductive substrate, The silver layer comprises a particle-containing metal layer covering at least a portion of the surface of the silver layer, The silver layer has a silver content of 50% by mass or more and 100% by mass or less, and a thickness of 1.0 μm or more. The thickness of the silver layer is 10 to 60% of the total thickness of the silver layer and the particle-containing metal layer. The particle-containing metal layer comprises a matrix made of a metal material and particles dispersed in the matrix. The aforementioned particles are made of an inorganic or organic material, and the average particle size is 1 / 2 or less of the thickness of the matrix, and the contact material.

2. The contact material according to claim 1, wherein the average particle size of the particles is 50 μm or less.

3. The contact material according to claim 1 or 2, wherein the particles include nonconductive particles.

4. The nonconductive particles have a fluoro group (-F) and a methyl group (-CH) within their unit molecular structure. ３ ), carbonyl group (-C(=O)-), amino group (-NR １ R ２ And R １ and R ２ R is a hydrogen or hydrocarbon group, １ and R ２ The contact material according to claim 3, wherein the particles are made of a nonconductive organic compound comprising one or more selected from the group consisting of a hydroxyl group (-OH), an ether bond (-O-), and an ester bond (-C(=O)-O-), which may be the same or different.

5. The contact material according to claim 1 or 2, wherein the matrix phase comprises one or more selected from the group consisting of silver and silver alloys.

6. The contact material according to claim 1 or 2, wherein the particle-containing metal layer satisfies the following formula (1). 2.0≦A ｐ / (A ｐ +A Ａｇ )×100≦12.0 ・・・(1) In equation (1), A ｐ A is the area of ​​the portion of the particles that is embedded in the matrix phase in a cross-section in the thickness direction of the contact material, Ａｇ This is the area of ​​the matrix phase in the cross-section in the thickness direction of the contact material.

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