Contact material

Abstract

This contact material comprises: an electroconductive substrate; a silver layer covering at least a portion of the surface of the electroconductive substrate; and a particle-containing metal layer covering at least a portion of the surface of the silver layer. The silver layer has a thickness of at least 1.0 μm. The particle-containing metal layer contains a base phase formed from a metal material and particles dispersed in the base phase.

Description

contact material

[0001] The present disclosure relates to contact materials.

[0002] CO ２ As emissions regulations become stricter, the number of electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs), which are less dependent on fossil fuels, is expected to increase. Because these vehicles require daily battery charging, the contact terminal materials connecting the vehicle to an external power source must be designed to withstand significantly more frequent insertion and removal than those used in conventional vehicles. Furthermore, shortening the charging process requires the passage of large currents. To minimize heat loss at the contacts, surface treatments with low surface contact resistance are required on both the vehicle body and power source sides. In this field, highly conductive (low contact resistance) silver (Ag) plating is often used. However, Ag plating generally has low hardness and is prone to "seizing" when sliding between Ag electrodes, resulting in rapid wear during repeated insertion and removal (sliding).

[0003] For this reason, current electric vehicle charging terminals require the formation of a significantly thicker Ag plating film (tens of μm thick) than the typical Ag plating film (several μm thick) applied to contact materials to prevent exposure of the base material even when wear occurs due to repeated insertion and removal (sliding). This increases the amount of Ag required for the terminal material, resulting in higher material costs. Furthermore, forming a thick Ag plating film using electroplating requires a long electroplating process, which also poses the problem of significantly reducing productivity.

[0004] To address these problems, it is known that a "particle eutectoid Ag plating film" in which particles of a non-conductive organic compound that have a wear-suppressing effect are contained in the Ag plating layer is effective (e.g., Patent Documents 1 and 2).

[0005] JP 2022-154356 A JP 2024-006857 A JP 2020-128575 A

[0006] When materials coated with a particle-eutectoid Ag plating film are subjected to processes such as bending and punching, the plating film is prone to cracking. The main reason for this is that the particle-plating interface in the particle-eutectoid Ag plating film is likely to be the crack initiation point. When cracks occur in a plating film provided on a contact material, although there is little adverse effect on the functionality of the contact material, there is the problem of a deterioration in the visual appearance. In particular, the occurrence of numerous coarse cracks significantly deteriorates the appearance and is disliked by users, so it is desirable to suppress the occurrence of coarse cracks.

[0007] Japanese Patent Laid-Open Publication No. 2020-128575 (Patent Document 3) discloses a terminal material for a connector (contact material) that can improve wear resistance, heat resistance, and crack resistance, and that includes 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. ３ By forming Pt intermetallic compounds, wear resistance and heat resistance are improved, and Ag ３ The crack resistance is improved by thinning the film thickness of the Pt intermetallic compound to 0.04 μm or more and 1.9 μm or less. However, since the platinum used in Patent Document 3 is expensive, there is a problem that the cost of the contact material increases.

[0008] The present invention has been made in view of the above circumstances, and one of its objects is to provide a contact material that can suppress the occurrence of large cracks and has sufficient wear resistance while suppressing manufacturing costs.

[0009] A first aspect of the present invention is 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.

[0010] A second aspect of the present invention is the contact material according to the first aspect, wherein the silver layer has a silver content of 50% by mass or more and 100% by mass or less.

[0011] A third aspect of the present invention is the contact material according to the first or second aspect, wherein the thickness of the silver layer is 10 to 60% of the total thickness of the silver layer and the particle-containing metal layer.

[0012] A fourth aspect of the present invention is the contact material according to any one of the first to third aspects, wherein the particles include non-conductive particles.

[0013] Aspect 5 of the present invention is characterized in that the non-conductive particles contain, in their unit molecular structure, a fluoro group (—F), a methyl group (—CH ３ ), a carbonyl group (—C(═O)—), an amino group (—NR １ R ２ and R １ and R ２ is 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] A sixth aspect of the present invention is the contact material according to any one of the first to fifth aspects, wherein the matrix phase contains at least one selected from the group consisting of silver and silver alloys.

[0015] A seventh aspect of the present invention is the contact material according to any one of the first to sixth aspects, 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 part of the particle buried in the matrix in a cross section of the contact material in the thickness direction, and A Ａｇ is the area of ​​the parent phase in a cross section of the contact material in the thickness direction.

[0016] According to the embodiments of the present invention, it is possible to provide a contact material that can suppress the occurrence of large cracks and has sufficient wear resistance while suppressing manufacturing costs.

[0017] Fig. 1 is a schematic cross-sectional view of an example of a contact material according to an embodiment of the present invention. Fig. 2 is a schematic cross-sectional view of another example of a contact material according to an embodiment of the present invention. Fig. 3A is a cross-sectional SEM image of a particle-eutectoid-plated sample of Sample No. 9 of Example 2, taken in a cross section in the thickness direction of the contact material. Fig. 3B is an image obtained by trimming only the particle-containing metal layer from Fig. 3A. Fig. 3C is a binarized image of Fig. 3B. Fig. 4A is a graph showing the relationship between the friction coefficient (□) and contact resistance (Δ) and the particle eutectoid ratio, obtained from the particle-eutectoid-plated sample of Sample No. 9 of Example 2. Fig. 4B is a graph showing the relationship between the friction coefficient (□) and contact resistance (Δ) and the particle eutectoid ratio, obtained from the particle-eutectoid-plated sample of Sample No. 10 of Example 2. Fig. 5A is a cross-sectional SEM image of a contact material sample after a bending test. Fig. 5B is an enlarged view of the area surrounded by the dashed line in Fig. 5A. Fig. 6A is a cross-sectional SEM image of a contact material sample after a bending test. Fig. 6B is an enlarged view of the portion surrounded by the dashed line in Fig. 6A. Fig. 7 is a cross-sectional SEM image of the contact material sample after the bending test. Fig. 8 is a cross-sectional SEM image of the contact material sample after the bending test.

[0018] 1 and 2 are schematic cross-sectional views in 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, and the silver layer 3 is substantially free of particles 2b.

[0019] The particle-containing metal layer 2 has particles 2b dispersed in a matrix 2a made of a metal material, and therefore has higher wear resistance than a metal layer that does not contain particles 2b. In other words, the contact materials 1 and 11 can have good wear resistance by including the particle-containing metal layer 2. Furthermore, because the particle-containing metal layer 2 includes a matrix 2a made of a metal material, the particle-containing metal layer 2 as a whole is conductive regardless of what kind of particles 2b are dispersed therein (for example, particles 2b made of conductive, non-conductive, inorganic, or organic materials).

[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 ductility. Furthermore, the silver layer 3 does not substantially contain particles 2b. Therefore, the silver layer 3 has the characteristic that cracks are unlikely to occur inside the silver layer 3 and, even if cracks do occur, they are unlikely to grow (crack resistance). The silver layer 3 may contain a small amount of particles 2b as long as the crack resistance is not impaired. For example, if the content of particles 2b is 1% by volume or less with respect to the entire silver layer 3 (including particles 2b), the wear resistance can be slightly improved without substantially deteriorating the crack resistance.

[0021] When tensile stress is applied to the particle-containing metal layer 2 due to processing of the contact materials 1, 11, etc., cracks may occur in the particle-containing metal layer 2, originating from particles 2b dispersed inside the particle-containing metal layer 2. These cracks grow further due to the tensile stress. Crack growth refers to the crack widening and extending 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 a cross section in the thickness direction of the contact materials 1, 11, they appear as wide cracks on the surface side of the particle-containing metal layer 2 that extend long from there toward the conductive substrate 4 (depth direction).

[0022] As the cracks that have occurred in the particle-containing metal layer 2 continue to grow, they attempt to cross the silver layer 3 and reach the conductive substrate 4. However, because the silver layer 3 has crack resistance, the cracks that extend in the depth direction can be stopped by the silver layer 3. When the extension of the crack in the depth direction stops (i.e., the growth of the crack stops), the crack width also stops expanding. In this way, by providing the silver layer 3 between the conductive substrate 4 and the particle-containing metal layer 2, the growth of the cracks that have occurred in the particle-containing metal layer 2 can be stopped, and therefore the occurrence of large cracks in the particle-containing metal layer 2 can be suppressed.

[0023] In this way, in the contact materials 1 and 11 according to the embodiments, 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 particle-containing metal layer 2 present on the surface side of the contact materials 1 and 11 can improve the wear resistance, and the silver layer 3 located between the particle-containing metal layer 2 and the conductive substrate 4 can prevent the occurrence of large cracks in the particle-containing metal layer 2. Unlike the contact materials 1 and 11 in the cited document 3, the contact materials 1 and 11 according to the embodiments do not require the use of platinum, and therefore can reduce manufacturing costs.

[0024] In addition, Patent Document 3 also discloses that a silver layer is provided between the substrate and the silver-platinum alloy layer, but this silver layer is Ag ３ It is provided as a silver source when forming an intermetallic compound of Pt, and is not provided with the intention of suppressing cracks with a silver layer.

[0025] The silver layer 3 of the contact materials 1 and 11 according to the embodiments is formed from a metal material containing silver as a main component, 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, and thereby the occurrence of coarse cracks in the particle-containing metal layer 2 can be more effectively suppressed.

[0026] The ratio of the thickness 3t of the silver layer 3 to the thickness 2t of the particle-containing metal layer 2 can affect the wear resistance and the effect of suppressing the occurrence of coarse cracks of the contact materials 1 and 11. Therefore, it is preferable to control the thickness ratio appropriately. In particular, the ratio of the thickness 3t of the silver layer 3 to the total thickness (3t + 2t) of the silver layer 3 and the particle-containing metal layer 2 (referred to as the "thickness ratio of the silver layer 3") is preferably 10 to 60%. A thickness ratio of the 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 the silver layer 3 of 60% or less can ensure a sufficient thickness 2t of the particle-containing metal layer 2, 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, and 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 in consideration of the balance with the particle-containing metal layer 2 formed on the contact materials 1, 11, but is at least 1.0 μm or more, and may be, for example, more than 1.0 μm but not more than 10 μm, preferably 1.2 μm or more, more preferably 1.5 μm or more, and preferably 5.0 μm or less, and more preferably 3.0 μm or less. Within this thickness range, the production costs of the contact materials 1, 11 can be reduced while providing sufficient crack resistance to the contact materials 1, 11. 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 may be, for example, 100 μm or less, or even 50 μm or less.

[0028] The thickness 3t of the silver layer 3 and the thickness 2t of the particle-containing metal layer 2 can be quantified from a cross-sectional SEM image of a cross section obtained by cutting a sample of the contact material 1, 11 in the thickness direction of the contact material 1, 11 (which substantially coincides with the direction perpendicular to the surface of the conductive substrate 4). The cross-sectional SEM image is taken at a magnification of 1000x, with the vertical direction of the observation field coinciding with the thickness direction of the contact material 1, 11. The field of view is, for example, 140 μm vertical × 200 μm horizontal.

[0029] In measuring the thickness 3t of the silver layer 3, first, in a cross-sectional SEM image, 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 identified. The distance between the first boundary and the second boundary in the direction perpendicular to the surface 4a of the conductive substrate 4 is measured, and this is defined as the "thickness 3t of the silver layer 3."

[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 may have a form in which some of the particles 2b protrude outward from the surface 2c of the matrix 2a, as shown in Fig. 1, or a form in which all of the particles 2b are completely buried in the matrix 2a, as shown in Fig. 2.

[0031] In the case of the particle-containing metal layer 2 having the form shown in FIG. 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 mother phase 2a are identified. The distance between the second boundary and the top of the most protruding particle 2b in the direction perpendicular to the surface 4a of the conductive substrate 4 is measured, and this is defined as the "thickness 2t of the particle-containing metal layer 2." Note that in the portion where no protruding particle 2b exists, that is, the portion where the surface 2c of the mother phase 2a is exposed, the "thickness 2at of the mother phase 2a" can be measured. The distance between the second boundary and the surface 2c of the mother phase 2a in the direction perpendicular to the surface 4a of the conductive substrate 4 is defined as the "thickness 2at of the mother phase 2a."

[0032] In the case of the particle-containing metal layer 2 having the form shown in FIG. 2 , the distance between the second boundary (surface 3a of the silver layer 3) and the surface 2c of the parent phase 2a is defined as the "thickness 2t of the particle-containing metal layer 2." In a cross-sectional SEM image, the second boundary and the surface 2c of the parent phase 2a are identified. The distance between the second boundary and the surface 2c of the parent phase 2a in the direction perpendicular to the surface 4a of the conductive substrate 4 is measured, and this is defined as the "thickness 2t of the particle-containing metal layer 2." Note that in the particle-containing metal layer 2 shown in FIG. 2 , the thickness 2at of the parent 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 may be calculated by arithmetic average of measurements taken at any two to five positions. However, in the case of the particle-containing metal layer 2 having the configuration shown in Figure 1, the "thickness 2t of the particle-containing metal layer 2" is measured at the position where the particles 2b protrude most, as described above.

[0034] The silver layer 3 and the particle-containing metal layer 2 can be distinguished from each other 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 includes a matrix 2 a made of a metal material and particles 2 b dispersed in the matrix 2 a. The dispersion state of the particles 2 b in the matrix 2 a can be roughly divided into two types (FIGS. 1 and 2).

[0037] In the contact material 1 of Fig. 1, most of the particles 2b are completely embedded in the matrix 2a. However, some of the particles 2b located near the surface 2c of the matrix 2a protrude outward from the surface 2c of the matrix 2a. In other words, some particles 2b are partially embedded in the matrix 2a and the remaining portions are exposed from the surface 2c of the matrix 2a near the surface 2c of the matrix 2a. When the wear resistance of the contact material 1 is improved by decomposition of the particles 2b, it is preferable that the particles 2b are partially exposed from the surface 2c of the matrix 2a, as shown in Fig. 1. This allows the particles 2b to be decomposed by insertion and removal (sliding) of the contact material 1 from the early stages of use, thereby improving the wear resistance.

[0038] In the contact material 11 of Fig. 2, all particles 2b are completely buried in the matrix 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. When the particles 2b are made of a non-conductive material, the particles 2b are not exposed from the surface 2c of the matrix 2a, as shown in Fig. 2, so that the electrical conductivity of the particle-containing metal layer 2 can be improved (contact resistance can be further reduced). Furthermore, the matrix 2a is worn away by insertion and removal (sliding) of the contact material 1, and the buried particles 2b are exposed, thereby improving wear resistance.

[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 includes 50% to 100% by mass of silver. The matrix 2a may include various silver platings (e.g., soft Ag plating, hard Ag plating, bright Ag plating, semi-bright Ag plating, etc.) commonly used in terminal surface treatments. Alternatively, a silver alloy plating may be used to improve the corrosion resistance (e.g., sulfur resistance) and wear resistance of the matrix 2a. Examples of silver alloys suitable for the silver alloy plating include Ag—Sn, Ag—Sb, and Ag—Cu.

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

[0041] 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 metal materials, the types or contents of alloy elements contained in the silver layer 3 and the matrix 2a differ, and therefore the silver layer 3 and the matrix 2a can be distinguished by element mapping using cross-sectional SEM-EDX analysis. In other words, the cross-sectional SEM-EDX analysis can distinguish the range of the silver layer 3 from the range of the particle-containing metal layer 2 including the matrix 2a.

[0042] When the silver layer 3 and the parent phase 2a are formed from the same metal material, it is not possible to distinguish between the silver layer 3 and the parent phase 2a by cross-sectional SEM-EDX analysis. Therefore, it is necessary to distinguish the range of the silver layer 3 from the range of the parent phase 2a (particle-containing metal layer 2) by another method. In this case, the region containing particles 2b is referred to as the "particle-containing metal layer 2," and the region not containing particles 2b is referred to as the "silver layer 3." As described above, the silver layer 3 may contain a small amount of particles 2b, but when the silver layer 3 and the parent phase 2a are formed from the same metal material, the silver layer 3 is considered not to contain particles 2b in order to make it easier to identify the first boundary.

[0043] The boundary (second boundary) between the silver layer 3 and the particle-containing metal layer 2 is identified in an SEM image of a cross section of the contact material 1, 11 in the thickness direction. The cross-sectional SEM image is subjected to image processing using a method described below to identify all of the particles 2b contained in the particle-containing metal layer 2. Of these particles 2b, the boundary (second boundary) between the silver layer 3 and the conductive substrate 4 is determined based on the particle 2b closest to the conductive substrate 4. That is, on the cross-sectional SEM image, the second boundary is drawn so that the particle 2b closest to the conductive substrate 4 is located closer to the particle-containing metal layer 2 than the second boundary, and so that this particle 2b contacts the second boundary. The second boundary on the cross-sectional SEM image is linear and drawn approximately parallel to the surface of the conductive substrate 4.

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

[0045] The non-conductive particles have a fluoro group (-F), a methyl group (-CH ３ ), a carbonyl group (—C(═O)—), an amino group (—NR １ R２ and R １ and R ２ is 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—).

[0046] Here, "organic compounds" refers to compounds containing carbon, including carbon monoxide, carbon dioxide, carbonates, hydrocyanic acid, cyanates, thiocyanates, and B ４ This term excludes compounds with simple structures such as C and SiC. For example, a silicone resin having a siloxane bond (—Si—O—Si—) in the main chain and organic groups in the side chains is considered to be included in the term “organic compound” in this specification.

[0047] The non-conductive organic compound forming the particles 2b contains the above-mentioned functional group, thereby improving the abrasion resistance of the particle-containing metal layer 2. Here, the term "unit molecular structure" refers to one repeating unit in the case of a polymer, or to an individual molecule in the case of a non-polymer.

[0048] Although the reason why the use of particles made of a non-conductive organic compound improves the wear resistance of the particle-containing metal layer 2 is unclear, the following mechanism is assumed. It is believed that, during sliding of the particle-containing metal layer 2, for example, part of the non-conductive organic compound decomposes and diffuses and migrates near the surface of the contact material, and / or part of the non-conductive organic compound reacts with the silver-containing layer near the surface of the contact material, thereby reducing the coefficient of friction near the surface of the contact material, thereby improving the wear resistance of the contact material. It is believed that the non-conductive organic compound has a particular functional group in its unit molecular structure, which is particularly effective in promoting the decomposition of the compound due to the influence of sliding. Furthermore, since the amount of decomposition products and reaction products is small and the proportion of particles made of a specific non-conductive organic compound in the silver-containing film is controlled to a predetermined value or less, sufficient conductivity is believed to be ensured.

[0049] The particle size of the particles 2b is preferably such that they can be dispersed within the matrix 2a of the particle-containing metal layer 2 and do not impair the conductivity of the particle-containing metal layer 2. For example, the particle size (equivalent circle diameter) of the particles 2b is less than the thickness 2 at of the matrix 2a. This prevents the particles 2b from protruding too much from the surface 2c of the matrix 2a and impairing electrical connection between the particle-containing metal layer 2 and the external terminals. Furthermore, the equivalent circle diameter of the particles 2b is more preferably sufficiently smaller than the thickness 2 at of the matrix 2a (e.g., 1 / 2 or less of the thickness 2 at of the matrix 2a), allowing the particles 2b to be completely embedded in the matrix 2a (however, this does not mean that all particles 2b are completely embedded, but rather that some particles 2b may be completely embedded in the matrix 2a). The average particle size (average equivalent circle diameter) of the particles 2b may be, for example, 50 μm or less, 10 μm or less, or 0.1 μm or more. The thickness 2 at of the matrix 2a is measured as described above.

[0050] The area of ​​the particles 2b (mainly non-conductive particles) in the particle-containing metal layer 2 and the matrix 2a, which can be confirmed in a cross-sectional SEM image, preferably 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 part of the particle buried in the matrix 2 in the cross section of the contact material 1, 11 in the thickness direction, and A Ａｇ is the area of ​​the parent phase 2 in the cross section of the contact material 1, 11 in the thickness direction.

[0051] Formula (1) means that the area ratio of the particles encapsulated in the particle-containing metal layer 2 is 2.0% to 12.0% with respect to the entire particle-containing metal layer 2. Note that, because the particle-containing metal layer 2 encapsulating particles 2b can be formed by a eutectoid plating method (a method in which particles are placed in a plating solution and electroplated while stirring), the area ratio of the encapsulated particles is sometimes referred to as the "eutectoid ratio of particles."

[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 the conductivity of the particle-containing metal layer 2. When the particle area ratio (volume ratio) 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 decrease in conductivity of the particle-containing metal layer 2 can be kept low. In other words, when the particle area ratio (volume ratio) is 2.0% to 12.0%, the particle-containing metal layer 2 can achieve both high levels of wear resistance and conductivity. The particle area ratio (particle co-deposition ratio) is more preferably 6.0% or more and more preferably 10.0% or less.

[0053] Area A of the parent phase 2a Ａｇ can be obtained by binarizing a cross-sectional SEM image of the contact material 1, 11 in a cross section in the thickness direction using image processing software (e.g., "ImageJ" or the like). Specifically, in the cross-sectional SEM image, the parent phase 2a may appear relatively bright (i.e., white) and the protective layer of the cross-sectional SEM sample may appear relatively dark (i.e., black). Therefore, for example, after binarization using an intermediate brightness between the parent phase 2a and the protective layer as a threshold, the area of ​​the bright part is determined as the area A of the parent phase 2a. Ａｇ When the cross-sectional SEM image shows irregularities on the upper surface of silver-containing layer 2 a, the area of ​​parent phase 2 a may be calculated by taking the average line of the irregularities as the boundary line between parent phase 2 a and an upper layer (for example, a protective layer of a cross-sectional SEM sample).

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

[0055] Within the scope of the present invention, the contact materials 1 and 11 may contain particles other than the non-conductive particles 2b. For example, the contact materials 1 and 11 may contain particles made of a non-conductive organic compound that does not contain the specific functional group described above, inorganic particles, or particles that are not embedded in the matrix phase 2a. The contact materials 1 and 11 may also contain conductive particles, but the fewer conductive particles they contain, the more preferable it is to prevent short circuits at the contact due to the conductive particles falling off. For example, the particles contained in the contact materials 1 and 11 preferably account for 50% or more by volume of the non-conductive particles 2b, more preferably 60% or more by volume, 70% or more by volume, 80% or more by volume, or 90% or more by volume, and even more preferably all (100% by volume) of the particles are non-conductive 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% in a cross section of the contact materials 1 and 11 in the thickness direction.

[0056] The contact materials 1 and 11 according to the embodiments of the present invention may contain other layers (e.g., a conductive substrate, a strike plating layer, etc.) in order to achieve the object 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 contact materials 1 and 11 according to the embodiments of the present invention, for example, a silver layer 3 is formed by plating on a substrate, and then a predetermined amount of particles 2b is dispersed in a silver (or silver alloy) plating solution, and a current is passed through the solution while stirring, thereby performing silver plating, thereby obtaining a contact material in which a predetermined amount of particles 2b are embedded (co-deposited) in the matrix 2a.

[0058] In the electroplating process in which particles 2b are dispersed in a plating solution, the following reactions (A) and (B) proceed simultaneously: (A) Reaction in which particles dispersed in the solution electrostatically or physically adsorb (contact) to the substrate surface; (B) Reaction in which a matrix 2a is deposited (grows) on the substrate surface. The particles 2b adsorbed in (A) are incorporated into the matrix 2a of (B), resulting in "eutectoid formation." Under conditions in which eutectoid plating proceeds steadily, the particles 2b adsorbed in the initial stage of the reaction are incorporated into the matrix 2a, while new particles 2b are simultaneously adsorbed. Therefore, even when the plating process is stopped, in many cases, the particles 2b remain exposed on the outermost surface. In a typical eutectoid plating process, a contact material 1 (see FIG. 1 ) can be easily produced, containing particles 2b that are partly embedded in the matrix 2a and the remaining partly exposed on the surface of the matrix 2a.

[0059] The amount of particles 2b co-deposited into the matrix 2a (e.g., the area ratio of particles 2b) is determined by the balance between the frequency of adsorption (A) and the growth rate of the plating film (B). Therefore, the amount of co-deposition can be changed by changing plating conditions, such as the amount of particles 2b dispersed in the plating solution. For example, by using a plating solution that does not contain particles 2b dispersed in the plating solution at the final stage of the plating process, or by changing the stirring speed of the plating solution to reduce the frequency of adsorption (A), a layer that prevents particles 2b from co-depositing can be formed on the outermost surface of the plating, thereby making it possible to produce a contact material 11 (see FIG. 1 ) in which all of the particles 2b are embedded in the matrix 2a.

[0060] The following examples are provided to more specifically describe the embodiments of the present invention. The embodiments of the present invention are not limited to the following examples, and may be modified as appropriate within the scope of the above-described and below-described aims, and all such modifications are within the technical scope of the embodiments of the present invention.

[0061] <Method for producing particle-coated plating> In order to easily identify the molecular structure conditions of particles that can provide excellent abrasion resistance, the abrasion resistance and conductivity of particle-coated Ag plating were evaluated. A pure copper plate with a thickness of 0.3 mm was used as the plating substrate, and after degreasing the surface with acetone, a commercially available strike Ag plating solution (Dyne Silver GPE-ST, manufactured by Daiwa Kasei Co., Ltd.) was used as the base for plating, and a Pt-coated Ti plate was used as the counter electrode at 5 A / dm ２ The substrate was then subjected to strike Ag plating treatment to a thickness of approximately 0.1 μm at a current density of 3 A / dm for 1 minute. The resulting plate was then used as the substrate. After that, a commercially available non-cyanide semi-gloss Ag plating solution (Daiwa Kasei Co., Ltd., Dyne Silver GPE-SB) was used, and a pure Ag plate was used as the counter electrode. ２ A current was passed through the plate at a current density of 1000 kJ / min for 5 minutes to form a semi-bright Ag plating layer approximately 10 μm thick. After plating, a suspension of particles shown in Tables 1 and 2 in alcohol was dropped onto the surface of the sample, and the sample was dried to prepare a sample for evaluating abrasion resistance. Note that the alcohol suspension of particles was not applied to Sample No. 1.

[0062] <Wear Resistance Evaluation Method> A hard Ag plating layer (Vickers hardness HV: approximately 165) of approximately 50 μm was formed on a 0.25 mm thick pure copper plate, and an embossed shape with R = 1.8 mm was formed by hand pressing. This sample was used as a mating material, and a friction sliding test was performed for up to 500 cycles between the sample for wear resistance evaluation (using a horizontal load tester 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) in each sliding cycle was measured, and the friction coefficient μ was read after 100, 300, and 500 cycles, respectively. A sample with μ ≦ 0.50 at 100 cycles was evaluated as "excellent," indicating particularly excellent friction improvement effect; a sample with μ ≦ 0.50 at 300 cycles was evaluated as "good," and a sample with μ > 0.50 at 500 cycles was evaluated as "fail." "Excellent" and "good" were evaluated as passing.

[0063] <Contact Resistance Test Method> The contact resistance at the contact points was measured using a Yamazaki Seiki Laboratory fretting wear tester for the wear marks after the friction test. The applied load was 5 N, and the average value measured at three locations was used for judgment as the contact resistance. Samples with a contact resistance of 0.500 mΩ or less after the friction test were judged to have "excellent contact resistance" and were deemed to have passed. Note that contact resistance measurements were not performed on samples whose wear resistance was unsatisfactory.

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

[0065]

[0066]

[0067] It was confirmed that Samples No. 2 to 8, which satisfy the requirements of the embodiment of the present invention, were able to maintain a low friction coefficient after 300 and 500 cycles of friction tests, and that the contact resistance after the friction tests was also good. Sample No. 1, which was the evaluation material, had a simple Ag plating layer and did not have the particle-containing metal layer 2, so it easily seized with the mating material and had poor wear resistance.

[0068] <Method for Preparing Particle-Eutectoid Plated Samples> To confirm the effect of the particle-containing metal layer 2, samples (particle-eutectoid plated samples) were prepared with particle-eutectoid plated layers in which particles were actually co-deposited into an Ag plating layer. The wear resistance and conductivity were evaluated by varying the particle co-deposition rate of the particle-eutectoid plated samples. 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 was dispersed in the plating solution, and electroplating was performed while stirring, resulting in 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 required to prevent the particles from agglomerating in the Ag plating layer and maintain a stable dispersion state. The obtained particle-eutectoid plated samples were subjected to friction tests and contact resistance measurements and evaluations using the same methods as in Example 1.

[0069] <Method of calculating particle deposition rate by observing plated cross section> The particle deposition rate of the obtained particle eutectoid-plated sample was calculated by the following formula (1): 2.0≦Aｐ / (A ｐ +A Ａｇ ) × 100≦12.0 (1) In formula (1), A ｐ is the area of ​​the part of the particle buried in the matrix in a cross section of the contact material in the thickness direction, and A Ａｇ is the area of ​​the parent phase in a cross section of the contact material in the thickness direction. Using a scanning electron microscope (SEM, Hitachi S-3500N), under conditions of an acceleration voltage of 20 kV and a working distance of 15 mm, cross-sectional SEM images (secondary electron images) of contact materials 1 and 11 were taken in the cross section in the thickness direction of particle eutectoid-plated samples coated with a protective layer for cross-sectional SEM, samples No. 10 and No. 11. Area A of parent phase 2 Ａｇ The cross-sectional SEM image was binarized using the image processing software "ImageJ" as described above, and the area of ​​the bright part was taken as the area of ​​the bright part. In the cross-sectional SEM image, the average line of the irregularities on the upper surface of the mother phase 2 was taken as the boundary line between the mother phase 2 and the protective layer of the cross-sectional SEM sample. The area A of the part of the plurality of particles buried in the silver-containing layer was taken as the area of ​​the part of the silver-containing layer. ｐ was defined as the area of ​​the dark portion (portion corresponding to the non-conductive organic compound) after the binarization process as described above, which was embedded in the mother phase 2. In the cross-sectional SEM image, the average line of the irregularities on the upper surface of the mother phase 2 was defined 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 defined as the portion embedded in the mother phase 2.

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

[0071] These analytical results were compiled to determine the range of particle co-deposition ratios that could achieve both wear resistance and electrical conductivity from the perspectives of friction coefficient and contact resistance (Figures 4A and 4B). Note that a particle co-deposition ratio that satisfied the criteria of "friction coefficient of 0.50 or less and contact resistance of 0.500 mΩ or less" was deemed acceptable. The measurement results are shown in Table 3.

[0072]

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

[0074] Sample No. 10 is a sample equipped with polyethylene oxide particle eutectoid plating. Figure 4B shows the relationship between the particle eutectoid ratio and the friction coefficient and contact resistance for Sample No. 10. With particle eutectoid plating with a particle eutectoid ratio of 0.5%, the friction coefficient after 20 sliding cycles dropped to approximately 0.2. Furthermore, at particle eutectoid ratios of 2.0% or higher, the friction coefficient stabilized at approximately 0.1. Contact resistance remained almost unchanged at approximately 0.3 mΩ for particle eutectoid ratios between 0% and 8.0%. It was confirmed that at particle eutectoid ratios of 0.5% or higher, good wear resistance and conductivity were achieved.

[0075] It can be said that the range of particle co-deposition ratio that can achieve both a low friction coefficient and low contact resistance varies depending on the type of particle.

[0076] <Method for creating two-layered plating structure for bending test> After degreasing the surface of a 0.3 mm thick pure copper plate by alkaline cleaning, a nickel sulfamate plating solution was used as a base treatment to prevent copper diffusion from the pure copper plate, and the plating was conducted at 5 A / dm ２For 90 seconds, a current density of 3 A / dm was applied to form a Ni plating layer with a thickness of approximately 1 μm. Next, as a base treatment to prevent Ag substitution reaction, a commercially available strike Ag plating solution (Dyne Silver GPE-ST manufactured by Daiwa Kasei Co., Ltd.) was used, and an iridium oxide-coated Ti plate was used as the counter electrode. ２ The wire was subjected to strike Ag plating treatment to a thickness of about 0.1 μm or less for 10 seconds at a current density of 1000 kJ / cm. The wire was then used as a substrate.

[0077] A commercially available non-cyanide semi-gloss Ag plating solution (Dyne Silver GPE-SB, manufactured by Daiwa Kasei Co., Ltd.) was used to form the silver layer 3 on the substrate, and a pure Ag plate was used as the counter electrode at 3 A / dm ２ A current was passed through the wire for 270 seconds at a current density of 1000 kJ / min, forming an Ag plating layer having a thickness of about 5 μm.

[0078] Next, a commercially available non-cyanide semi-bright Ag plating solution (Dainsilver GPE-SB manufactured by Daiwa Kasei Co., Ltd.) was used to form the particle-containing metal layer 2. A surfactant (Surflon S231 manufactured by AGC Seimi Chemical Co., Ltd.) was added to the solution, and then the particles shown in Table 4 were added. While stirring, a pure Ag plate was used as the counter electrode and a current of 3 A / dm ２ The current was passed for 270 seconds at a current density of 1000 kJ / s, forming a particle-deposited Ag plating layer having a thickness of approximately 5 μm. The ratio of the thickness of the silver layer 3 to the total thickness of the silver layer 3 and the particle-containing metal layer 2 was 50%.

[0079] Using these procedures, contact material samples (Samples Nos. 11 and 12) were obtained that had a silver layer 3 (pure Ag) and a particle-containing metal layer 2 in which particles were co-deposited (embedded). For comparison, a contact material sample (Sample No. 13) in which only the particle-containing metal layer 2 was formed (i.e., the silver layer 3 was not formed) and a contact material sample (Sample No. 14) in which only the silver layer 3 was formed (i.e., the particle-containing metal layer 2 was not formed) were also prepared.

[0080]

[0081] <Method for Evaluating Bending Workability> The obtained contact material samples (Samples No. 11 to 14) were cut into 10 mm widths and subjected to bending tests. A W-bend test jig conforming to JIS H 3110 was used for the bending test. An R of 0.5 mm was used. To check for cracking in the cross section of the bent portion of the sample, the cross section at the apex of the 90° bend in the bending test was observed. A scanning electron microscope (SEM: BRUKER-Hitachi, QUANTAX) was used to obtain cross-sectional SEM images (secondary electron images) at a magnification of 1000x, an acceleration voltage of 20 kV, and a working distance of 15 mm. The field of view was 140 μm vertically and 200 μm horizontally, and the silver layer 3 and particle-containing metal layer 2 at the apex of the 90° bend were observed.

[0082] In the obtained cross-sectional SEM images, cracks were determined to be present if they satisfied the following conditions A to D. In the cross-sectional SEM images, the silver layer 3 and the parent phase 2a of the particle-containing metal layer 2 are observed as white or light gray areas, while the particles 2b of the particle-containing metal layer 2, the cracks, and the embedding resin (used to prepare the cross-sectional observation sample) are observed as dark gray areas.

[0083] A. A dark gray portion located inside (on the conductive substrate 4 side) the surface line of the particle-containing metal layer 2 and exposed from the surface of the particle-containing metal layer 2. B. A portion having an area of ​​2π (μm ２ ) or more. C. The entire crack is visible within the field of view. D. The dimension in the direction perpendicular to the surface 4a of the conductive substrate 4 (the length of the crack) is 2 μm or more. If the surface 4a of the conductive substrate 4 is curved, the tangent to the point on the surface 4a at which the perpendicular direction is to be defined is taken 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) of the particle-containing metal layer 2. This is because cracks observed from the surface deteriorate the appearance when viewed from above the particle-containing metal layer 2. Condition B is a condition for excluding particles 2b. Since particles 2b have a D50 of 2 μm, in the cross-sectional SEM image, the area is π (μm ２It is estimated that the particle 2b is observed as a dark gray particulate area of ​​about 2π (μm). Taking into account the variation in particle diameter of the particle 2b, the area is assumed to be twice the estimated area, that is, 2π (μm ２ ) are regarded as "particles 2b" and are not cracks. Condition D is for excluding 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 positions on the crack, and the largest value among these (maximum crack width) is identified. 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 a cross-sectional SEM image. When 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 is determined based on the contact point between the inner surface of the crack and the surface 4a of the conductive substrate 4. Because 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 determined as the crack width measurement direction.

[0086] The specimens with the maximum crack width of 10 μm or more were judged as "poor," those with the maximum crack width of less than 10 μm were judged as "good," and those with no cracks were judged as "excellent." When the judgment was "good" or "excellent," the bending workability was judged as "passed," and when the judgment was "poor," the bending workability was judged as "failed."

[0087] Fig. 5A is a cross-sectional SEM image of the apex of a 90° bend of a contact material sample of Sample No. 11 in Table 3 after a bending test, showing that cracks were generated. As shown in Fig. 5B, the maximum crack width was 4.4 μm (good), and the bending workability was "pass." Fig. 6A is a cross-sectional SEM image of the apex of a 90° bend of a contact material sample of Sample No. 12 in Table 3 after a bending test, showing that cracks were generated. As shown in Fig. 6B, the maximum crack width was 1.5 μm (good), and the bending workability was "pass." Fig. 7 is a cross-sectional SEM image of the apex of a 90° bend of a contact material sample of Sample No. 13 in Table 3 after a bending test, showing that cracks were generated. Because the silver layer 3 was not formed, the maximum crack width was 19.2 μm (poor), and the bending workability was "fail." Fig. 8 is a cross-sectional SEM image of Sample No. 12 in Table 3 after a bending test, showing that cracks were generated. 10 is a cross-sectional SEM image of the apex of a 90° bend after a bending test was performed on contact material sample No. 14. Since no particle-containing metal layer 2 was provided, no cracks occurred (bendability evaluation: excellent).

[0088] This application claims priority from Japanese Patent Application No. 2024-073052, filed April 26, 2024. Japanese Patent Application No. 2024-073052 is incorporated herein by reference.

[0089] 1, 11 Contact material 2 Particle-containing metal layer 2a Mother phase 2b Particle (non-conductive particle) 2c Surface of mother phase 3 Silver layer 3a Surface of silver layer 4 Conductive substrate 4a Surface of conductive substrate

Claims

1. 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.

2. The contact material according to claim 1, wherein the silver layer has a silver content of 50% by mass or more and 100% by mass or less.

3. The contact material according to claim 1, wherein the thickness of the silver layer is 10 to 60% of the total thickness of the silver layer and the particle-containing metal layer.

4. The contact material according to any one of claims 1 to 3, wherein the particles include non-conductive particles.

5. The non-conductive particles have a fluoro group (-F), a methyl group (-CH) in the unit molecular structure. ３ ), a carbonyl group (—C(═O)—), an amino group (—NR １ R ２ and R １ and R ２ is 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—).

6. The contact material according to any one of claims 1 to 3, wherein the matrix phase contains at least one material selected from the group consisting of silver and silver alloys.

7. The contact material according to any one of claims 1 to 3, 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 part of the particle buried in the matrix in a cross section of the contact material in the thickness direction, and A Ａｇ is the area of ​​the parent phase in a cross section of the contact material in the thickness direction.

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