JP7794885B2 - contact material - Google Patents

Description

This disclosure relates to contact materials.

As _CO2 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 a large current. 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 plates, resulting in wear that progresses easily during repeated insertion and removal (sliding).

For this reason, current electric vehicle charging terminals require the formation of a significantly thicker Ag plating film (tens of microns thick) than the typical Ag plating film (several microns thick) applied to contact materials to prevent the base material from being exposed 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 issue of significantly reducing productivity.

To address these issues, it is known that a "particle eutectoid Ag plating film," in which particles of a non-conductive organic compound with wear-suppressing effects are incorporated into the Ag plating layer, is effective (see, for example, Patent Documents 1 and 2).

Japanese Patent Application Laid-Open No. 2022-154356 Japanese Patent Application Laid-Open No. 2024-006857 Japanese Patent Application Laid-Open No. 2020-128575

When a material coated with a particle-eutectoid Ag plating film is subjected to processing such as bending or 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 become the starting point for cracks.
When cracks occur in the plating film provided on the contact material, they have little adverse effect on the functionality of the contact material, but they can cause a problem of poor visual appearance. In particular, when many large cracks occur, the appearance deteriorates significantly, which makes users dislike the product, so it is desirable to suppress the occurrence of large cracks.

Japanese Patent Laid-Open Publication No. 2020-128575 (Patent Document 3) discloses a connector terminal material (contact material) that can improve wear resistance, heat resistance, and crack resistance, which 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. The silver layer and the silver-platinum alloy layer are reacted to form an _Ag3Pt intermetallic compound, thereby improving wear resistance and heat resistance, and the film thickness of the _Ag3Pt intermetallic compound is reduced to 0.04 μm or more and 1.9 μm or less, thereby improving crack resistance.
However, since the platinum used in Patent Document 3 is expensive, there is a problem in that the cost of the contact material increases.

The present invention was made in light 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 that has sufficient wear resistance.

Aspect 1 of the present invention is
A conductive substrate;
a silver layer covering at least a portion of the surface of the conductive substrate;
a particle-containing metal layer covering at least a portion of the surface of the silver layer;
the silver layer has a thickness of 1.0 μm or more,
The particle-containing metal layer is a contact material that includes a matrix made of a metal material and particles dispersed in the matrix.

Aspect 2 of the present invention is
In the contact material according to aspect 1, the silver layer has a silver content of 50% by mass or more and 100% by mass or less.

Aspect 3 of the present invention is
A contact material according to aspect 1 or 2, 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.

Aspect 4 of the present invention is
Aspect 4. The contact material according to any one of aspects 1 to 3, wherein the particles include non-conductive particles.

Aspect 5 of the present invention is
A contact material according to Aspect 4 is a particle made of a non-conductive organic compound containing, in its unit molecular structure, one or more selected from the group consisting of a fluoro group (-F), a methyl group (-CH ₃ ), 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-).

Aspect 6 of the present invention is
Aspect 6 is the contact material according to any one of Aspects 1 to 5, wherein the matrix phase contains at least one selected from the group consisting of silver and silver alloys.

Aspect 7 of the present invention is
7. 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 part of the particle buried in the matrix in the cross section of the contact material in the thickness direction, and A _Ag is the area of the matrix in the cross section of the contact material in the thickness direction.

Embodiments of the present invention make it possible to provide a contact material that suppresses the occurrence of large cracks while keeping manufacturing costs down and that has sufficient wear resistance.

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. 3A is a cross-sectional SEM image of a particle eutectoid-plated sample of Example 2, Sample No. 9, taken in the thickness direction of the contact material. FIG. 3B is an image of FIG. 3A in which only the particle-containing metal layer is cropped. FIG. 3C is a binarized image of FIG. 3B. 4A is a graph showing the relationship between the particle eutectoid ratio and the coefficient of friction (□) and contact resistance (Δ), as determined from the particle eutectoid-plated sample of Sample No. 9 in Example 2. 4B is a graph showing the relationship between the particle eutectoid ratio and the friction coefficient (□) and contact resistance (Δ), which were determined from the particle eutectoid-plated sample of Sample No. 10 in Example 2. FIG. 5A is a cross-sectional SEM image of a contact material sample after bending testing. FIG. 5B is an enlarged view of the area enclosed by the dashed line in FIG. 5A. FIG. 6A is a cross-sectional SEM image of a contact material sample after bending testing. FIG. 6B is an enlarged view of the area enclosed 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.

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. 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.

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, 11 are provided with good wear resistance by having a particle-containing metal layer 2. Furthermore, because the particle-containing metal layer 2 contains a matrix 2a made of a metal material, the particle-containing metal layer 2 as a whole is conductive regardless of the type of particles 2b dispersed therein (e.g., particles 2b made of conductive, non-conductive, inorganic, or organic materials, etc.).

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 whose main component is silver and has excellent ductility. Furthermore, the silver layer 3 is substantially free of particles 2b. Therefore, the silver layer 3 is characterized by the fact that cracks are unlikely to occur within 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 relative to the entire silver layer 3 (including particles 2b), abrasion resistance can be slightly improved without substantially deteriorating crack resistance.

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 within 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, grown cracks appear as wide cracks (referred to as "coarse cracks"). Furthermore, when observed in a cross section through the thickness 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).

If a crack that has occurred 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 the crack from extending in the depth direction. When the extension of the crack in the depth direction (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 crack that has occurred in the particle-containing metal layer 2 can be stopped, thereby preventing the occurrence of large cracks in the particle-containing metal layer 2.

In this way, in contact materials 1 and 11 according to the embodiments, by laminating the silver layer 3 and 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 contact materials 1 and 11 can improve 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 Cited Document 3, contact materials 1 and 11 according to the embodiments do not require the use of platinum, thereby reducing manufacturing costs.

Although Patent Document 3 also discloses that a silver layer is provided between the substrate and the silver-platinum alloy layer, this silver layer is provided as a silver source for forming an Ag ₃ Pt intermetallic compound, and is not provided with the intention of suppressing cracks by the silver layer.

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 primary component, such as pure silver or a silver alloy. In other words, 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, which more effectively prevents the occurrence of large cracks in the particle-containing metal layer 2.

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, 11. Therefore, it is preferable to control the thickness ratio to an appropriate value.
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%. When the thickness ratio of the silver layer 3 is 10% or more, the occurrence of large cracks in the particle-containing metal layer 2 can be more effectively suppressed. When the thickness ratio of the silver layer 3 is 60% or less, the thickness 2t of the particle-containing metal layer 2 can be sufficiently ensured, and the wear resistance of the contact materials 1, 11 can be further improved.
The thickness ratio of the silver layer 3 is more preferably 15% or more, even more preferably 20% or more, and is preferably 50% or less, more preferably 45% or less, even more preferably 40% or less, and particularly preferably 30% or less.

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 and not more than 10 μm, preferably not less than 1.2 μm, more preferably not less than 1.5 μm, and preferably not more than 5.0 μm, more preferably not more than 3.0 μm. If the thickness is within this 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 appropriately depending on the application, but may be, for example, 100 μm or less, or even 50 μm or less.

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 (substantially coincident 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 x 200 μm horizontal.

To measure 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."

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

In the case of the particle-containing metal layer 2 having the form shown in FIG. 1 , the distance between the second boundary (surface 3 a of the silver layer 3) and the top of the protruding particle 2 b is defined as the "thickness 2 t of the particle-containing metal layer 2." In a cross-sectional SEM image, the second boundary and the particle 2 b that protrudes most from the surface 2 c of the parent phase 2 a are identified. The distance between the second boundary and the top of the most protruding particle 2 b in the direction perpendicular to the surface 4 a of the conductive substrate 4 is measured, and this is defined as the "thickness 2 t of the particle-containing metal layer 2."
In addition, in a portion where no protruding particles 2 b are present, that is, a portion where the surface 2 c of the mother phase 2 a is exposed, the “thickness 2 at” of the mother phase 2 a can be measured. The distance between the second boundary and the surface 2 c of the mother phase 2 a in the direction perpendicular to the surface 4 a of the conductive substrate 4 is the “thickness 2 at” of the mother phase 2 a.

In the case of the 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 parent phase 2a is defined as the "thickness 2t of the particle-containing metal layer 2." The second boundary and the surface 2c of the parent phase 2a are identified in a cross-sectional SEM image. 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."
In the particle-containing metal layer 2 shown in FIG. 2, the thickness 2 at of the matrix 2 a is equal to the thickness 2 t of the particle-containing metal layer 2 .

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 two to five positions and the arithmetic average of the measurement results may be used. However, in the case of a particle-containing metal layer 2 having the form 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 explained above.

The silver layer 3 and the particle-containing metal layer 2 can be distinguished using the method described below.

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.

As described above, the particle-containing metal layer 2 includes a matrix 2a made of a metal material and particles 2b dispersed in the matrix 2a. The dispersion states of the particles 2b in the matrix 2a can be broadly divided into two types (Figures 1 and 2).

In the contact material 1 of 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 portions exposed from the surface 2c of the matrix 2a. If the wear resistance of the contact material 1 is improved by, for example, decomposition of the particles 2b, it is preferable that the particles 2b be partially exposed from the surface 2c of the matrix 2a, as shown in Figure 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.

2, all of the particles 2b are completely embedded in the matrix 2a, meaning that the particles 2b cannot be directly observed even when observing the particle-containing metal layer 2 from the surface side.
When the particles 2b are made of 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 2a, as shown in Fig. 2. Furthermore, the matrix 2a is worn away by the insertion and removal (sliding) of the contact material 1, and the buried particles 2b are exposed, thereby improving wear resistance.

The metallic 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, 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 silver alloy plating include Ag-Sn, Ag-Sb, and Ag-Cu.

In addition, using pure silver plating for the parent phase 2a makes it possible to obtain a particle-containing metal layer 2 with excellent conductivity. The parent phase 2a may contain silver in the range of 90% by mass to 100% by mass, 95% by mass to 100% by mass, or 99% by mass to 100% by mass.

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 makes it possible to distinguish between the range of the silver layer 3 and the range of the particle-containing metal layer 2 that includes the matrix 2a.

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, another method is required to distinguish between the extent of the silver layer 3 and the extent of the parent phase 2a (particle-containing metal layer 2). 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 mentioned above, the silver layer 3 may contain trace amounts 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.

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 the method described below to identify all 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. In other words, 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 is in contact with 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.

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 due to wear of the particle-containing metal layer 2. If the particles 2b are non-conductive particles, this is advantageous because there is a low possibility of a short circuit occurring even if the particles 2b fall off and accumulate near the contact.
Here, "non-conductive" means that it does not exhibit conductivity, and for example, refers to a material whose volume resistivity measured in accordance with ASTM D257 is approximately 10 ³ [Ω·cm] or more.

The non-conductive particles are preferably particles made of a non-conductive organic compound that contains, in its unit molecular structure, one or more selected from the group consisting of a fluoro group (-F), a methyl group (-CH ₃ ), 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-).

Here, "organic compounds" refers to compounds containing carbon, excluding compounds with simple structures such as carbon monoxide, carbon dioxide, carbonates, hydrocyanic acid, cyanates, thiocyanates, _B4C , 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 "organic compounds" in this specification.

By including the functional groups described above in the non-conductive organic compound that forms the particles 2b, the wear resistance of the particle-containing metal layer 2 can be improved. Here, "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.

The reason why the use of particles made of a non-conductive organic compound can improve the wear resistance of the particle-containing metal layer 2 is not clear, but the following mechanism is assumed.
This is thought to be because, 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 lowering the coefficient of friction near the surface of the contact material, thereby improving the wear resistance of the contact material. It is thought that the non-conductive organic compound having a specific functional group in its unit molecular structure is particularly effective in promoting the decomposition of the compound due to the influence of sliding. Furthermore, since the amount of decomposed and reacted products is small, and the proportion of particles made of the specific non-conductive organic compound in the silver-containing film is controlled to a predetermined value or less, sufficient conductivity is thought to be ensured.

The particle size of the particles 2b is preferably such that they can be dispersed in 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 (circle-equivalent 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 the electrical connection between the particle-containing metal layer 2 and the external terminals. Furthermore, it is more preferable that the circle-equivalent diameter of the particles 2b is sufficiently smaller than the thickness 2 at of the matrix 2a (for example, ½ 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 the particles 2b are completely embedded, but rather that some particles 2b may be completely embedded in the matrix 2a).
The average particle size (average circle equivalent 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 2at of the parent phase 2a is measured as described above.

The area of the particles 2b (mainly non-conductive particles) and the matrix 2a in the particle-containing metal layer 2 that 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 matrix 2 in the cross section of the contact material 1, 11 in the thickness direction.

Equation (1) means that the area ratio of the particles encapsulated in the particle-containing metal layer 2 is 2.0% to 12.0% of the entire particle-containing metal layer 2. Note that because the particle-containing metal layer 2 encapsulating particles 2b can be formed by eutectoid plating (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 "particle eutectoid ratio."

The particles contained in the particle-containing metal layer 2 contribute to the wear resistance of the particle-containing metal layer 2, but also 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.

The area A _Ag of the mother phase 2 a can be determined 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 mother phase 2 a 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 mother phase 2 a and the protective layer as a threshold, the area of the bright portion can be determined as the area A _Ag of the mother phase 2 a. Note that if the cross-sectional SEM image shows irregularities on the upper surface of the silver-containing layer 2 a, the area of the mother phase 2 a may be determined by using the average line of the irregularities as the boundary line between the mother phase 2 a and an upper layer (e.g., the protective layer of the cross-sectional SEM sample).

On the other hand, the area _Ap of the portion of particle 2b buried in mother phase 2a can be defined as the area of the dark portion after binarization (the portion corresponding to the non-conductive organic compound in the case of a non-conductive particle) buried in mother phase 2a. If there are irregularities on surface 2c of mother phase 2a in the cross-sectional SEM image, the average line of the irregularities is taken as the boundary line between mother phase 2a and an upper layer (e.g., a protective layer of a cross-sectional SEM sample), and the portion below this average line is defined as the portion buried in mother phase 2a.

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 groups 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 contacts due to the conductive particles falling off. For example, it is preferable that 50% or more by volume of the particles contained in the contact materials 1 and 11 be 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 that all (100% by volume) 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.

Contact materials 1 and 11 according to embodiments of the present invention may contain other layers (e.g., a conductive substrate, a strike-plated layer, etc.) to achieve the object of the present invention. For example, in 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).

Contact materials 1 and 11 according to embodiments of the present invention are prepared by, for example, plating a silver layer 3 on a substrate, dispersing a predetermined amount of particles 2b in a silver (or silver alloy) plating solution, and then conducting a silver plating process while stirring and passing an electric current through the solution, thereby obtaining a contact material in which a predetermined amount of particles 2b are embedded (co-deposited) in the matrix 2a.

In the process of electroplating with particles 2b dispersed in a plating solution, the following reactions (A) and (B) proceed simultaneously.
(A) A reaction in which particles dispersed in a liquid electrostatically or physically adsorb (contact) onto the substrate surface. (B) A reaction in which a matrix 2a is deposited (grows) onto the substrate surface. The particles 2b adsorbed in (A) are incorporated into the matrix 2a of (B), resulting in "eutectoid." Under conditions in which eutectoid plating steadily progresses, the particles 2b adsorbed in the initial stage of the reaction are incorporated into the matrix 2a, and at the same time, new particles 2b are adsorbed. For this reason, even when the plating process is stopped, in many cases the particles 2b are exposed on the outermost surface. In a typical eutectoid plating process, it is possible to easily produce a contact material 1 (see Figure 1) containing particles 2b that are partly embedded in the matrix 2a and the remaining partly exposed on the surface of the matrix 2a.

Here, the amount of co-deposition of particles 2b into the matrix 2a (e.g., 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-deposition 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 toward the end of the plating process, or by changing the stirring speed of the plating solution to reduce the adsorption frequency of (A), a layer that prevents particles 2b from co-deposition can be formed on the outermost surface of the plating, making it possible to produce a contact material 11 (see Figure 1) in which all particles 2b are embedded in the matrix 2a.

The following examples will explain the embodiments of the present invention in more detail. The embodiments of the present invention are not limited to the following examples, and may be implemented with appropriate modifications within the scope of the above-mentioned and below-mentioned aims, all of which are within the technical scope of the embodiments of the present invention.

<Method for producing particle-coated plating>
In order to easily identify the molecular structure conditions of particles that can provide excellent wear resistance, the wear resistance and conductivity of Ag plating coated with the particles were evaluated.
A 0.3 mm thick pure copper plate was used as the plating substrate. After degreasing the surface with acetone, a commercially available strike Ag plating solution (Dainsilver GPE-ST, manufactured by Daiwa Kasei Co., Ltd.) was used as the base for plating. A Pt-coated Ti plate was used as the counter electrode, and a current density of 5 A/ ^dm² was applied for 1 minute to form a strike Ag plating layer approximately 0.1 µm thick. This was then used as the substrate. A commercially available non-cyanide semi-bright Ag plating solution (Dainsilver GPE-SB, manufactured by Daiwa Kasei Co., Ltd.) was then used as the counter electrode, and a pure Ag plate was used as the counter electrode, and a current density of 3 A/ ^dm² was applied for 5 minutes to form a semi-bright Ag plating layer approximately 10 µm thick.
After plating, a liquid prepared by suspending particles shown in Tables 1 and 2 in alcohol was dropped onto the surface of the sample, followed by drying to prepare a sample for evaluating abrasion resistance. Note that, for Sample No. 1, the alcohol suspension of particles was not applied.

<Wear resistance evaluation method>
A 0.25 mm thick pure copper plate was coated with a 50 μm thick hard Ag plating (Vickers hardness HV: approximately 165), and a hand press was used to create an embossed sample with a radius of 1.8 mm. A friction sliding test was conducted for up to 500 cycles between the sample and the abrasion resistance evaluation sample (using an Aiko Engineering horizontal load tester). 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. Tests with μ≦0.50 at 100 cycles were rated "excellent" as being particularly excellent in terms of friction improvement effect, tests with μ≦0.50 at 300 cycles were rated "good," and tests with μ>0.50 at 500 cycles were rated "fail." Tests with "excellent" and "good" ratings were rated as passing.

<Contact resistance test method>
The contact resistance at the contact points was measured using a Yamazaki Seiki Laboratory fretting wear tester, focusing on 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 for which wear resistance was unsatisfactory.

The above results are summarized in Table 2.

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 testing, and also had good contact resistance after the friction testing.
In Sample No. 1, the evaluation material was a simple Ag plating layer and did not have the particle-containing metal layer 2, so seizure easily occurred between the evaluation material and the mating material, and the wear resistance was poor.

<Method for preparing particle eutectoid plating samples>
In order to confirm the effect of the particle-containing metal layer 2, samples (particle eutectoid-plated samples) were prepared that had particle-eutectoid plating layers in which particles were actually co-deposited in an Ag plating layer, and the wear resistance and electrical conductivity were evaluated by varying the particle co-deposition rate of the particle eutectoid 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 was dispersed in a 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 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 a friction test and contact resistance measurement evaluation in the same manner as in Example 1.

<Method for calculating particle deposition rate by observing the plating cross section>
The particle co-deposition rate of the obtained particle co-deposition plated sample was calculated by the following formula.
Using a scanning electron microscope (SEM, Hitachi S-3500N) at an accelerating 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 at cross sections in the thickness direction for particle eutectoid-plated samples coated with a protective layer for cross-sectional SEM of samples No. 10 and 11. The area A _Ag of the mother phase 2 was determined as the area of the bright portion after the cross-sectional SEM images were binarized as described above using the image processing software "ImageJ." In the cross-sectional SEM image, the mean line of the irregularities on the upper surface of the mother phase 2 was taken as the boundary between the mother phase 2 and the protective layer of the cross-sectional SEM sample. The area A _p of the portions of the multiple particles buried in the silver-containing layer was determined as the area of the dark portion (corresponding to the non-conductive organic compound) buried in the mother phase 2 after the binarization as described above. 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 particle-containing metal layer 2 and the protective layer of the cross-sectional SEM sample, and the part below this average line was taken as the part buried in the mother phase 2.

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 plating sample for Sample No. 9, produced with a particle dispersion amount of 3 g/L in the liquid. Figure 3B is an image of Figure 3A in which only the mother phase 2 (and particles embedded in mother phase 2) has been cropped, and Figure 3C is a binarized image of Figure 3B. When the area of the black portion in Figure 3C was divided by the area of Figure 3B, the area ratio (particle co-deposition ratio) was 2.51%.

These analysis results were compiled to determine the range of particle co-deposition ratio that would achieve both wear resistance and electrical conductivity from the perspective 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.

Sample No. 9 is a sample equipped with cross-linked 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. With particle eutectoid plating with a particle eutectoid ratio of 2.0% to 12.0%, the friction coefficient after 20 sliding cycles remained stable at around 0.4, and contact resistance remained below 0.500 mΩ, confirming that good wear resistance and conductivity were achieved.

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, and 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 over the particle eutectoid ratio range of 0% to 8.0%. It was confirmed that at particle eutectoid ratios of 0.5% or higher, good wear resistance and conductivity were both achieved.

The range of particle co-deposition ratios that can achieve both a low friction coefficient and low contact resistance can vary depending on the type of particle.

<Method for creating two-layer plating structure for bending test>
The surface of a 0.3 mm thick pure copper plate was degreased by alkaline cleaning, and then a Ni sulfamate plating solution was used as a base treatment to prevent copper diffusion from the pure copper plate. A current was passed through the plate at a current density of 5 A/ ^dm² for 90 seconds 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 (Dainsilver GPE-ST manufactured by Daiwa Kasei Co., Ltd.) was used. An iridium oxide-coated Ti plate was used as the counter electrode, and a current density of ³ A/dm2 was applied for 10 seconds to perform strike Ag plating to a thickness of approximately 0.1 μm or less. This was used as the substrate.

A commercially available non-cyanide semi-gloss Ag plating solution (Dynesilver GPE-SB, manufactured by Daiwa Kasei Co., Ltd.) was used to plate the substrate as the silver layer 3. A current was applied for 270 seconds at a current density of ³ A/dm² using a pure Ag plate as the counter electrode, to form an Ag plating layer having a thickness of approximately 5 µm.

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 current was passed through the solution at a current density of 3 A/ ^dm2 for 270 seconds using a pure Ag plate as the counter electrode, forming a particle-eutectoid Ag plating layer with 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%.

By these procedures, contact material samples (samples Nos. 11 and 12) having a silver layer 3 (pure Ag) and a particle-containing metal layer 2 in which particles are co-deposited (embedded) were obtained.
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.

<Method for evaluating bending workability>
The obtained contact material samples (samples No. 11 to 14) were cut into pieces with a width of 10 mm and subjected to a bending test using a W-bending test jig in accordance with JIS H 3110. In this test, R = 0.5 mm was used.
To check for cracking in the cross section of the bent portion of the sample, the cross section of the apex of the 90° bend in the bending test was observed. A scanning electron microscope (SEM: BRUKER-Hitachi, QUANTAX) was used to obtain a cross-sectional SEM image (secondary electron image) at a magnification of 1000x, an acceleration voltage of 20 kV, and a work distance of 15 mm. The field of view was 140 μm vertically × 200 μm horizontally, and the silver layer 3 and the particle-containing metal layer 2 at the apex of the 90° bend were observed.

In the obtained cross-sectional SEM images, cracks were determined to be found if they satisfied the following conditions A to D. In the cross-sectional SEM images, the silver layer 3 and the matrix 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, cracks, and embedding resin (used to prepare the cross-sectional observation sample) are observed as dark gray areas.

A. A dark gray portion located inside the surface line of the particle-containing metal layer 2 (on the conductive substrate 4 side) and exposed from the surface of the particle-containing metal layer 2.
B. The area is 2π (μm ² ) or more.
C. The entire crack is visible within the field of view.
D. The dimension (crack length) in the direction perpendicular to the surface 4a of the conductive substrate 4 is 2 μm or more. If the surface 4a of the conductive substrate 4 is curved, the perpendicular direction is specified by taking the tangent at the point on the surface 4a to which the perpendicular direction is to be defined as the "surface 4a."

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 in a plan view of the particle-containing metal layer 2 deteriorate the appearance.
Condition B is a condition for excluding particles 2b. Since particles 2b have a D50 of 2 μm, they are estimated to be observed as dark gray particulate areas with an area of approximately π (μm ² ) in cross-sectional SEM images. Taking into account the variation in particle diameter of particles 2b, dark gray areas with an area of less than 2π (μm ² ), which is twice the estimated area, are considered to be "particles 2b" and not cracks.
Condition D is for eliminating minute irregularities on the surface of the particle-containing metal layer 2 .

Once the crack was identified, the crack width was measured at various positions on the crack, and the largest value (maximum crack width) was 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. If the surface 4a of the conductive substrate 4 is not flat and the direction in which to measure the crack width cannot be determined unambiguously on the cross-sectional SEM image, the measurement direction was determined based on the point of contact 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 points of contact between the inner surface of the crack and the surface 4a of the conductive substrate 4. The direction parallel to the line connecting these points of contact was used to measure the crack width.

Cracks with a maximum width of 10 μm or more were rated as poor, cracks with a maximum width of less than 10 μm were rated as good, and cracks without any occurrence were rated as excellent. If the rating was good or excellent, the bending workability was rated as "passed," and if the rating was poor, the bending workability was rated as "failed."

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

1, 11 Contact material 2 Particle-containing metal layer 2a Mother phase 2b Particles (non-conductive particles)
2c: Surface of parent phase 3: Silver layer 3a: Surface of silver layer 4: Conductive substrate 4a: Surface of conductive substrate

Claims (7)

A conductive substrate;
a silver layer covering at least a portion of the surface of the conductive substrate;
a particle-containing metal layer covering at least a portion of the surface of the silver layer;
a Ni layer between the conductive substrate and 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 particle-containing metal layer includes a matrix made of a metal material and particles dispersed in the matrix,
The particles are made of an inorganic material or an organic material and have an average particle size of 1/2 or less of the thickness of the matrix . 2. The contact material according to claim 1, wherein the average particle size of said particles is 50 [mu]m or less . 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. The contact material described in any one of claims 1 to 3, wherein the particles include non-conductive particles. 5. The contact material according to claim ₄ , wherein the non-conductive particles are particles made of a non-conductive organic compound containing, in its unit molecular structure, ^one or more selected from the ^group consisting of a fluoro group (-F), a methyl group (-CH ³ ), 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-). The contact material according to any one of claims 1 to 3, wherein the parent phase contains one or more materials selected from the group consisting of silver and silver alloys. 4. The contact material according to claim 1, 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 matrix in a cross section of the contact material in the thickness direction.