Self-lubricating coating, manufacturing method, and electrical contact

Abstract

To provide a self-lubricating composition for a coating for high-current contacts, as well as for an inexpensive, simplified, and reliable method for their manufacturing with which the contact surface of an electrical connector is treated such that a further reduction in the plugging force and a low contact resistance are obtained.SOLUTION: A self-lubricating coating is provided, including a dispersion system made of sulfur-containing nanoparticles incorporated into a silver matrix, wherein the sulfur-containing nanoparticles have a composition of Ag2S and / or Au2S. The present invention furthermore relates to a self-lubricating coating comprising a dispersion system made of fluorinated graphene, and / or carbon nanotube (CNT), and / or carbon nanoparticles of the formula (CF)x incorporated into a silver matrix, wherein the fluorinated graphene, CNT, or carbon nanoparticles of the formula (CF)x have a fluorine to carbon ratio of 1 to 1.25.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a self-lubricating coating, a method for producing the coating, and an electrical contact comprising such a coating. [Background technology]

[0002] Electrical connectors are known in numerous configurations. Electrical connectors are intended to establish an electrical connection in a plugged-in state. Electrical connectors are generally used for either signal transmission or power transmission. For this purpose, electrical connectors typically comprise conductive contact elements that come into contact with each other when the connectors are plugged in. The contact elements of one connector element are often configured as contact pins, while the contact elements of the mating part are configured as a socket, either in one part or in two parts with inserted contact springs. When the connector and socket are plugged in, the contact springs exert a resilient spring force on the contact pins, ensuring a reliable conductive connection.

[0003] Electrical connectors are used to transfer energy and interconnect electrical and electronic systems, for example in automobiles, where they are exposed to severe temperature fluctuations, vibration, moisture, and corrosive media. Increased operating temperatures can cause increased contact resistance, especially for the commonly used tin-plated copper-based contact elements.

[0004] Silver coatings have been proposed, especially for high-current contact elements. This provides desirable electrical properties, such as low electrical resistance and contact resistance. Pure silver coatings have good electrical properties but unfavorable tribological properties. This can lead to contact problems when connector elements are frequently plugged in or when vibration loads occur. Therefore, a silver sulfide film, so-called "blue silver," has been proposed as an additional coating on top of the silver coating. This initially results in reduced insertion force and a consistently low contact resistance. Alternatively, graphite particles may be added to the silver coating to achieve improved wear behavior and a permanently low contact resistance.

[0005] However, known dispersions with graphite particles are difficult to use to make the coating or to handle during subsequent processing, which makes the coating process complicated, limited and more expensive.

[0006] Furthermore, it has been proposed to add particles made of hexagonal boron nitride (hBN), silicon carbide (SiC), or tungsten(IV) sulfide (WS2) to silver coatings in order to obtain improved wear behavior and low contact resistance. However, these additives do not sufficiently demonstrate the desired improvement in the electrical properties of electrical contacts thus coated. Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, there is a need for self-lubricating compositions for electrical contacts, preferably coatings for high current contacts, and inexpensive, simple, and reliable methods for their manufacture, in which the contact surfaces of electrical connectors are treated to provide further reductions in insertion force and low contact resistance. [Means for solving the problem]

[0008] This object is solved by the subject matter of the independent claims. Advantageous further developments of the invention are the subject matter of the dependent claims.

[0009] For a better understanding of the invention, it will be described in more detail with reference to the embodiments shown in the following drawings, in which the same parts are given the same reference numerals and component names. Furthermore, some features or combinations of features in the various embodiments shown and described may themselves represent independent, inventive or inventive solutions. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing an example of a silver coating having an Ag2S coating. [Figure 2] FIG. 1 is a diagram showing an example of a silver coating having dispersed graphite particles. [Figure 3] FIG. 1 shows an example of a silver coating with dispersed nanoparticles according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] In accordance with the present invention, in one embodiment, there is provided a self-lubricating coating comprising a dispersion made of sulfur-containing nanoparticles incorporated into a silver matrix. The sulfur-containing nanoparticles are selected from AgS and / or AuS. The sulfur-containing nanoparticles are dispersed in the silver matrix and are therefore uniformly distributed in the coating formed therefrom.

[0012] Figure 1 shows a silver coating 1 with a AgS coating 2, known from the prior art. Figure 2 shows an example of a silver coating 3 with dispersed graphite particles 4. For comparison, Figure 3 shows a silver coating 5 with dispersed nanoparticles 6 according to the invention. These nanoparticles 6 can be, for example, sulfur-containing nanoparticles or fluorinated carbon nanoparticles, such as fluorinated graphene, carbon nanotubes (CNTs), or nanoparticles of the formula (CF) x The carbon nanoparticles are

[0013] The sulfur-containing nanoparticles are contained as a dispersion in an amount of preferably 0.01 to 10% by volume, more preferably 0.1 to 8% by volume, and even more preferably 0.5 to 6% by volume, based on 100% by volume of the coating. The sulfur-containing nanoparticles impart self-lubricating properties to the coating.

[0014] The sulfur-containing nanoparticles preferably have an average particle size (average particle size) D50 of 20 to 150 nm, more preferably an average particle size D50 of 40 to 120 nm, and even more preferably an average particle size D50 of 50 to 90 nm. The average particle size D50 may be determined using the method described in DIN ISO 9276-2:2018-09.

[0015] According to the present invention, the present invention provides a fluorinated graphene, carbon nanotube (CNT), or nanoparticle of formula (CF) incorporated into a silver matrix. x In a further embodiment, the self-lubricating coating comprises a silver-based dispersion coating composed of carbon nanoparticles of the formula (CF) having a fluorine to carbon ratio of 1 to 1.25. x Carbon nanoparticles of the formula (CF) having a fluorine to carbon ratio of at least 1 to 1.25 may be used. The fluorinated graphene, CNT, or carbon nanoparticles are dispersed in the silver matrix and therefore uniformly distributed in the coating formed therefrom. xFluorinated carbon nanoparticles of the formula (CF) exhibit excellent thermal stability, do not corrode in strong alkaline and acidic environments, and exhibit excellent self-lubricating properties. x fluorinated carbon nanoparticles exhibit significantly poor thermal stability and are therefore unsuitable as lubricants.

[0016] The fluorinated nanoparticles are contained in the dispersion in an amount of preferably 0.01 to 10% by volume, more preferably 0.1 to 8% by volume, and even more preferably 0.1 to 5% by volume, based on 100% by volume of the coating. The fluorinated carbon nanoparticles impart self-lubricating properties to the coating.

[0017] The fluorinated carbon nanoparticles preferably have a bimodal particle size distribution, the bimodal distribution being 5 nm to 10 nm and 50 nm to 10 μm or 20 nm to 50 nm and 100 nm to 15 μm.

[0018] Formula (CF) x The fluorinated carbon nanoparticles preferably have a fluorine to carbon ratio of 1.0 or greater, more preferably 1 to 1.25.

[0019] The coating is of the formula (CF) incorporated into a silver matrix. x Preferably, the carbon nanoparticles are

[0020] Formula (CF) x The particle concentration of the carbon nanoparticles is preferably 0.01 to 5% by weight of the coating.

[0021] In the above embodiment, the silver particles are preferably contained in an amount of 90 to 99.9% by volume based on 100% by volume of the coating.

[0022] The coatings according to the present invention advantageously exhibit improved wear behavior while maintaining the low contact resistance of pure silver.

[0023] Furthermore, the self-lubricating coating may comprise a dispersant. Suitable dispersants are of polar origin, and preferred dispersants are nitrogen-containing organic solvents such as N-methylpyrrolidone.

[0024] The present invention also provides a coating comprising a layer comprising silver and nanoparticles, the nanoparticles being sulfur-containing nanoparticles selected from AgS and AuS, or nanoparticles of the formula (CF): x fluorinated carbon nanoparticles having a fluorine to carbon ratio of 1 to 1.25.

[0025] The coating may comprise sulfur-containing nanoparticles selected from Ag2S and Au2S, or a fluorine-to-carbon ratio of the formula (CF) having a fluorine-to-carbon ratio of 1 to 1.25. x Preferably, the carbon nanoparticles are

[0026] The coating may further comprise at least one intermediate layer, preferably made of nickel, pure silver or copper, preferably having a thickness of 0.5 to 4 micrometers, more preferably 1.0 to 3 micrometers, above which the dispersion-containing silver layer has a layer thickness of 0.5 to 25 μm, more preferably 0.5 to 4 μm or 5 to 25 μm.

[0027] Additionally, the coating may comprise a multilayer system comprising additional layers in addition to the layer comprising silver and the layer produced together with the coating according to the present invention. According to a further advantageous embodiment, the intermediate layer comprises tin, and / or nickel or NiP (nickel phosphorus), and / or silver, and / or copper, and / or an alloy of tin, nickel, silver, and copper. These materials are rust-resistant and heat-resistant, which ensures a long service life of the connector. Preferably, the intermediate layer comprises nickel, and the upper intermediate layer comprises silver. Each intermediate layer preferably has a thickness of 0.5 to 4 micrometers, more preferably 1.0 to 3 micrometers.

[0028] Advantageously, coatings produced with the coating according to the present invention exhibit improved wear behavior while maintaining the low contact resistance of pure silver.

[0029] The present invention further provides an electrical contact comprising a coating according to the present invention.

[0030] The present invention finally provides a method for producing a coating according to the present invention, which comprises coating a substrate with a coating according to the present invention. In particular, the present invention comprises a method for the surface treatment of conductive contact elements for electrical connectors, the conductive contact elements having a metallic contact surface. In addition, the coating according to the present invention is applied to at least a partial region of the contact surface of the conductive contact element.

[0031] The coating is preferably produced by electrodeposition or by physical vapor deposition using PVD, CVD or plasma deposition.

[0032] The Ag2S or Au2S nanoparticles are preferably masked to establish a positive zeta potential in the pH range of the coating bath. This is necessary to avoid aggregation or undesired chemical reactions between the particles, and as a result of electrical attraction, codeposition of the nanoparticles at the cathode occurs in the silver matrix. Process analysis methods such as photon correlation spectroscopy (PCS) and laser Doppler anemometry (LDA) are required for controlled deposition.

[0033] The coatings of the present invention exhibit excellent wear resistance and low contact resistance while simplifying coating methods and processing. The coatings of the present invention also have excellent electrical properties that make them particularly suitable for high current contacts.

[0034] The coating according to the invention allows for the simultaneous plugging of electrical contacts with multiple plug connections, up to 50,000 connector cycles, applications with high vibration loads and application temperatures of up to 200° C. The plug connections may be any type of plug connection already known in the prior art. [Explanation of symbols]

[0035] 1 silver coating 2 Ag2S coating 3. Silver coating with dispersed particles 4. Graphite particles 5. Silver coating with dispersed nanoparticles 6. Nanoparticles

Claims

1. a dispersion made of sulfur-containing nanoparticles incorporated into a silver matrix, the sulfur-containing nanoparticles being Ag ２ A self-lubricating coating having a composition of S.

2. 2. The self-lubricating coating according to claim 1, wherein the sulfur-containing nanoparticles are contained in the dispersion in an amount of 0.01 to 10% by volume, based on 100% by volume of the dispersed coating.

3. 2. The self-lubricating coating of claim 1, wherein the sulfur-containing nanoparticles have an average particle size D50 of 5 to 300 nm.

4. 2. The self-lubricating coating of claim 1, wherein the sulfur-containing nanoparticles have an average particle size D50 of 50 to 90 nm.

5. 2. The self-lubricating coating of claim 1, wherein the silver content in the silver matrix is ​​present in an amount of 90 to 99.99% by volume, based on 100% by volume of the dispersed coating.

6. The self-lubricating coating of claim 1 , further comprising a dispersant.

7. 7. The self-lubricating coating of claim 6, wherein the dispersant is selected from the group of polar dispersants.

8. The dispersion has the formula (CF) ｘ Fluorinated carbon nanoparticles of claim 1.

9. 10. The self-lubricating coating of claim 1, further comprising an additional layer comprising nickel, nickel phosphorus, copper, or pure silver, the additional layer having a thickness of 1 to 4 micrometers.

10. The self-lubricating coating of claim 1, wherein the self-lubricating coating comprises two intermediate layers between a layer comprising silver and the layer made using the self-lubricating coating of claim 1 or 5, the two intermediate layers including a first intermediate layer and a second intermediate layer, the first intermediate layer comprising nickel and having a thickness of 0.5 to 4 micrometers, and the second intermediate layer comprising silver and having a thickness of 0.5 to 4 micrometers.

11. An electrical contact comprising the self-lubricating coating of claim 1 .

12. 10. A method for producing the self-lubricating coating of claim 1, comprising coating a substrate with the self-lubricating coating of claim 1.

13. The method of claim 12, wherein the self-lubricating coating is produced by electrodeposition.

14. 13. The method of claim 12, wherein the self-lubricating coating is produced by physical vapor deposition using PVD (physical vapor deposition), CVD (chemical vapor deposition) or plasma deposition.

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