A composite coating for tantalum surfaces and a method for producing the same

Abstract

The present application belongs to the technical field of tantalum capacitor cathode current lead-out layer, and relates to a composite coating on a tantalum surface and a preparation method thereof, which comprises a base carbon layer, a porous carbon layer and a silver layer, and comprises the following steps: uniformly mixing a solvent, MMA and an initiator, defoaming to obtain a base carbon paste, coating the base carbon paste on the surface of a tantalum core, and solidifying to obtain the base carbon layer; uniformly mixing a solvent, MMA, polyethylene glycol-1500, a carbon conductive agent and an initiator, defoaming to obtain a pore-forming carbon paste, coating the pore-forming carbon paste on the base carbon layer, solidifying and pore-forming to form the porous carbon layer; uniformly mixing bisphenol A epoxy resin, a curing agent, a curing catalyst, a solvent and a silver conductive agent, defoaming to obtain a silver paste, coating the silver paste on the porous carbon layer, and solidifying to obtain the silver layer, thereby obtaining the composite coating; the composite coating can reduce the resistance value, and in turn, the ESR value of the tantalum capacitor.

Description

Technical Field

[0001] This invention belongs to the technical field of cathode current lead-out layer of tantalum capacitors, and relates to a composite coating on the surface of tantalum and its preparation method, which is used to prepare a composite coating with low resistance on the surface of tantalum core to reduce the ESR value of tantalum capacitors. Background Technology

[0002] In the fabrication of tantalum capacitors, carbon paste and silver paste are sequentially coated onto a tantalum core with manganese dioxide deposited on its surface. After the carbon paste cures, a carbon layer is formed, and after the silver paste cures, a silver layer is formed. These carbon and silver layers form a composite coating attached to the surface of the tantalum core to draw out the cathode current. In this composite coating, the carbon layer not only conducts electricity but also prevents direct contact between the silver layer and the tantalum core. Therefore, the carbon layer has a relatively dense structure, limiting the penetration of silver paste into it. This results in a limited contact area between the silver and carbon layers, leading to a higher interfacial resistance between them, which is detrimental to reducing the ESR value of the tantalum capacitor.

[0003] Chinese patent document CN118299184A discloses a capacitor with a polymer tantalum thin film and its fabrication process, including the following steps: using tantalum powder and tantalum wire as raw materials, pressing, sintering, and energy-enhancing treatment are performed to obtain an anode tantalum core; the anode tantalum core is subjected to cathode treatment to obtain a substrate; a graphite layer and a silver paste layer are sequentially coated on the outer surface of the substrate, and positive and negative electrodes are led out using a lead frame to obtain the capacitor. In this patent, the simple superposition of the graphite layer and the silver paste layer is used as the cathode current lead-out layer. The effective contact area between the graphite layer and the silver paste layer is limited, resulting in a high interface resistance, which is not conducive to further reducing the overall ESR value of the tantalum capacitor.

[0004] Chinese patent document CN118315199A discloses a high-capacity thin-film tantalum electrolytic capacitor and its manufacturing process. The capacitor includes a tantalum anode core, on which a Ta2O5 thin film, a manganese dioxide layer, and a graphite layer are sequentially disposed. A silver paste layer is disposed outside the graphite layer, comprising modified nano-silver powder, bisphenol A epoxy resin, a curing agent, ethyl acetate, and an active diluent. The silver shell formed by curing the silver paste layer is used to fix and connect the negative electrode lead. This patent uses graphite and polymer silver paste as the cathode lead material, and the silver paste layer uses modified nano-silver powder as the conductive material to improve the conductivity of the silver shell. However, the contact between the silver paste layer and the graphite layer is still a two-dimensional point-to-surface or surface-to-surface contact, limiting the effective contact area and hindering further reduction of the overall ESR value of the tantalum capacitor.

[0005] Chinese patent application CN108962421A discloses an impregnated silver paste and a tantalum capacitor. The process involves coating a tantalum core with an impregnated graphite paste and an impregnated silver paste sequentially. The impregnated graphite paste comprises graphite, carbon black, a polymer resin carrier, and a solvent. The impregnated silver paste comprises a polymer resin carrier, silver powder, graphite, carbon black, and a solvent. After curing, the impregnated graphite paste forms a carbon layer, and after curing, the impregnated silver paste forms a silver layer. The carbon layer and the silver layer constitute a composite coating attached to the surface of the tantalum core. Because the silver powder, carbon black, and graphite in the silver layer are uniformly mixed, the contact area between silver and carbon is increased. However, the conductivity of the silver layer depends on the continuous electron transport channels formed between the silver powder particles. The addition of graphite and carbon black reduces the density of the silver powder, hindering direct contact between the silver powder particles. Furthermore, the conductivity of graphite and carbon black is much lower than that of silver, resulting in a relatively high resistance value for the silver layer in the aforementioned patent application. This increases the overall resistance value of the composite coating and is detrimental to reducing the ESR value of the tantalum capacitor. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and solve the technical problem that the small contact area between the carbon layer and the silver layer is not conducive to reducing the ESR value of tantalum capacitors, and to provide a composite coating on the tantalum surface and its preparation method.

[0007] To achieve the above-mentioned objective, this invention provides a method for preparing a composite coating on a tantalum surface, wherein the composite coating comprises a base carbon layer, a porous carbon layer, and a silver layer, and the process includes the following steps:

[0008] S1. The solvent, MMA and initiator are mixed evenly, and a carbon conductive agent is added for dispersion. After degassing, a base carbon paste is obtained and coated on the surface of the tantalum core. The paste is then heated and cured to form a base carbon layer. The carbon conductive agent is prepared by mixing MPS-modified carbon black and MPS-modified graphite.

[0009] S2. Mix the solvent, MMA, polyethylene glycol-1500 and initiator, add carbon conductive agent to disperse, degas to obtain pore-forming carbon paste and coat it on the base carbon layer, heat to cure and form pores, forming a porous carbon layer on the base carbon layer.

[0010] S3. Bisphenol A epoxy resin, curing agent, curing catalyst and solvent are mixed evenly, silver conductive agent is added for dispersion, and after degassing, silver paste is obtained and coated on porous carbon layer. The mixture is heated and cured to form a silver layer on the porous carbon layer, thereby obtaining a composite coating. The silver conductive agent is obtained by modifying silver powder with epoxy silane.

[0011] This invention constructs a composite coating by sequentially coating a tantalum core surface with a base carbon paste, a pore-forming carbon paste, and a silver paste. The base carbon paste does not contain a pore-forming agent, and after curing, a dense base carbon layer is obtained, effectively preventing the subsequently coated silver paste from contacting the tantalum core. The pore-forming carbon paste contains polyethylene glycol-1500 as a pore-forming agent. After the polyethylene glycol-1500 is removed by heating, pores are formed in situ, resulting in a porous carbon layer. The silver paste is then coated on the porous carbon layer. Under capillary action, the silver paste penetrates into the pores of the porous carbon layer, achieving three-dimensional interpenetrating contact between the silver powder and the carbon conductive agent, increasing the contact area between the silver powder and the carbon conductive agent. After the silver paste cures, a silver layer is formed. The silver layer and the porous carbon layer are connected by a mechanical interlocking method, resulting in strong interfacial bonding, preventing the silver layer from falling off, and maintaining the structural integrity of the composite coating. At the same time, the carbon conductive agent and the silver powder are in two different coatings, and a continuous conductive path is formed between the silver powder particles, which is beneficial for obtaining a composite coating with low resistance and reducing the ESR value of the tantalum capacitor.

[0012] The carbon conductive agents involved in this invention include MPS-modified carbon black and MPS-modified graphite. After modification, methacryloyloxy functional groups are introduced on the surface of the carbon black and graphite. As the temperature increases, under the initiation of the initiator, MMA undergoes a copolymerization reaction with the methacryloyloxy functional groups on the surface of the carbon conductive agent, which bonds and fixes adjacent carbon conductive agent particles, improves the mechanical strength of the porous carbon layer, inhibits crack generation, and maintains the structural integrity of the composite coating, so that the ESR value and insulation resistance value of the tantalum capacitor remain stable during long-term use.

[0013] The carbon conductive agent of this invention is prepared by the following method: carbon black is dispersed in a 30-40 wt% nitric acid solution and reacted for 25-30 min. After washing, it is dispersed in MPS hydrolysate and reacted for 2-3 h. After washing, it is dried under reduced pressure to obtain MPS modified carbon black. Graphite is dispersed in a 30-40 wt% nitric acid solution and reacted for 35-40 min. After washing, it is dispersed in MPS hydrolysate and reacted for 2-3 h. After washing, it is dried under reduced pressure to obtain MPS modified graphite. The MPS modified carbon black and MPS modified graphite are mixed to obtain the carbon conductive agent. The washing liquid is deionized water and anhydrous ethanol.

[0014] This invention uses nitric acid solution to treat carbon black and graphite, which can increase the hydroxyl density on the surface of carbon conductive agents, thereby increasing the density of methacryloxy functional groups on the surface of MPS-modified carbon black and MPS-modified graphite, providing a molecular basis for subsequently improving the interfacial bonding force between carbon conductive agents through covalent bonds.

[0015] The MPS hydrolysate of the present invention is prepared by the following method: 95-96 wt% ethanol solution and MPS are mixed, acetic acid solution is added dropwise to adjust the pH value to 4-5, and the reaction is carried out for 3-4 hours to obtain the MPS hydrolysate.

[0016] In step S1 of this invention, the solvents EGBE, MMA and initiator AIBN are mixed, a carbon conductive agent is added for dispersion, and the mixture is placed in a 25-30 kPa environment for static degassing for 30-40 min to obtain a base carbon paste, which is then coated onto the surface of the tantalum core. The temperature is raised to 65-75℃ and held for 30-50 min, then raised to 165℃-170℃ and held for 35-50 min, and finally cooled to obtain a base carbon layer.

[0017] After two stages of heating, the MMA and the methacryloyloxy functional groups on the surface of the carbon conductive agent react fully under the thermal initiation of the initiator, bonding adjacent carbon conductive agent particles together. The uncrosslinked MMA and EGBE are volatilized and removed, resulting in a dense base carbon layer that effectively prevents the silver paste from contacting the tantalum core.

[0018] In step S2 of this invention, the solvents EGBE, MMA, polyethylene glycol-1500, and initiator AIBN are mixed and dispersed with a carbon conductive agent. The mixture is then allowed to stand for 30-40 minutes in a 25-30 kPa environment to degas, resulting in a porous carbon paste. This paste is then coated onto a substrate carbon layer. The mixture is heated to 65-75°C and held for 30-50 minutes, then heated to 120-130°C and held for 1-2 hours. The mixture is then placed in a nitrogen atmosphere and maintained at 230-240°C and 5-8 Pa for 1-1.5 hours. After cooling, a porous carbon layer is obtained on the substrate carbon layer. Under the conditions of 230-240°C and 5-8 Pa, polyethylene glycol-1500 in the porous carbon paste can be effectively volatilized and removed, and pores can be formed in situ, forming a porous carbon layer. This provides a structural basis for the subsequent infiltration of silver paste into the porous carbon layer.

[0019] In step S2 of this invention, the solvent, MMA, polyethylene glycol-1500, initiator, MPS hydrolysate, and p-toluenesulfonic acid are mixed. MPS can be hydrolyzed to generate silanol containing silanol and methacryloxy groups. This silanol can copolymerize with MMA and the methacryloxy functional groups on the surface of the carbon conductive agent under the initiator, and can also undergo a condensation reaction to generate siloxane bonds under the catalysis of p-toluenesulfonic acid, further improving the interfacial bonding force between carbon conductive agent particles, thereby improving the mechanical strength of the porous carbon layer.

[0020] The silver conductive agent of the present invention is prepared by the following method: KH-560 is mixed with 95-96wt% ethanol solution, acetic acid solution is added dropwise to adjust the pH value to 4-5, the reaction is carried out for 20-30 min, silver powder is added and dispersed, the reaction is carried out for 2-3 h, filtered, washed with anhydrous ethanol and dried under reduced pressure to obtain the silver conductive agent; the silver powder includes flake silver powder and spherical silver powder.

[0021] In step S3 of this invention, bisphenol A epoxy resin, curing agent MTHP, curing catalyst EMI-24 and solvent EGBE are mixed evenly, silver conductive agent is added for dispersion, and the mixture is placed in a 25-30 kPa environment for static degassing for 30-40 min to obtain silver paste, which is then coated onto a porous carbon layer. The mixture is left to stand for 45-55 min, heated to 70-75℃ and held for 40-50 min, and then heated to 120-130℃ and held for 1-2 h to form a silver layer on the porous carbon layer, thus obtaining a composite coating.

[0022] This invention also provides a composite coating for a tantalum surface, prepared by the above-described method for preparing a composite coating for a tantalum surface. The base carbon layer comprises the following parts by weight: MMA 9-12 parts, EGBE 10-15 parts, carbon conductive agent 5-9 parts, and AIBN 0.01-0.02 parts; the porous carbon layer comprises the following parts by weight: MMA 5-9 parts, EGBE 7-12 parts, polyethylene glycol-1500 4-7 parts, AIBN 0.01-0.02 parts, p-toluenesulfonic acid 0-0.03 parts, MPS hydrolysate 0-1 parts, and carbon conductive agent 6-9 parts; the silver layer comprises the following parts by weight: bisphenol A epoxy resin 15-18 parts, MTHP 5-6 parts, EMI-24 0.2-0.3 parts, and EGBE... 6-8 parts, silver conductive agent 82-86 parts; the MPS hydrolysate includes the following raw materials by weight: 300-310 parts of 95-96wt% ethanol solution, 9-11 parts of MPS.

[0023] The carbon conductive agent of the present invention comprises 16-18 parts by weight of MPS modified carbon black and 7-9 parts by weight of MPS modified graphite; the MPS modified carbon black comprises the following parts by weight of raw materials: 16-20 parts of carbon black and 150-160 parts of MPS hydrolysate; the MPS modified graphite comprises the following parts by weight of raw materials: 9-12 parts of graphite and 90-100 parts of MPS hydrolysate; the silver conductive agent comprises the following parts by weight of raw materials: 2-3 parts of KH-560, 300-310 parts of 95-96wt% ethanol solution, 28-30 parts of flake silver powder, and 40-44 parts of spherical silver powder.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects: First, the prepared composite coating includes a base carbon layer formed by curing a base carbon paste, a porous carbon layer formed by curing a pore-forming carbon paste, and a silver layer formed by curing a silver paste. The base carbon layer is relatively dense, effectively preventing the silver paste from contacting the tantalum core. The porous carbon layer contains pores formed in situ after the volatilization and removal of polyethylene glycol-1500. The silver paste penetrates into the pores under capillary action, increasing the contact area between the silver and the carbon conductive agent. The silver layer and the carbon layer are connected by mechanical interlocking, making the silver layer less prone to falling off. After the silver layer is cured, it forms a continuous conductive path, reducing the resistance value of the composite coating and thus reducing the ESR value of the tantalum capacitor. Second, after the carbon conductive agent is treated with MPS hydrolysate, methacryloxy functional groups are introduced on its surface. These functional groups can react with MMA under the thermal initiation of the initiator, connecting adjacent carbon conductive agents through covalent bonds, improving the mechanical strength of the porous carbon layer, and keeping the ESR value of the tantalum capacitor at a low level during long-term use, thus improving the long-term stability of the tantalum capacitor. Detailed Implementation

[0025] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments.

[0026] Example 1:

[0027] In this embodiment, 9g of MPS (γ-methacryloyloxypropyltrimethoxysilane) was added to 300g of 95wt% ethanol solution, stirred at 300rpm for 10min, and the pH was adjusted to 5 by adding 10wt% acetic acid solution dropwise. The mixture was stirred at 300rpm for 3.5h to obtain MPS hydrolysate. 18g of carbon black with a particle size of 30nm was added to 100g of 30wt% nitric acid solution, ultrasonically dispersed at 300W for 25min, filtered, washed with deionized water until the eluent was neutral, washed twice with anhydrous ethanol, added to 150g of MPS hydrolysate, stirred at 3200rpm for 10min, stirred at 600rpm for 3h, filtered, washed twice with deionized water, washed twice with anhydrous ethanol, and dried at 40℃ and 12.1kPa for 5h to obtain MPS-modified carbon black. 9g of graphite with a particle size of 2μm was added to 100g of... In a 30wt% nitric acid solution, the mixture was ultrasonically dispersed at 300W for 35 min, filtered, washed with deionized water until the eluent was neutral, washed twice with anhydrous ethanol, added to 90g of MPS hydrolysate, stirred at 3200rpm for 10 min, then stirred at 600rpm for 3 h, filtered, washed twice with deionized water, washed twice with anhydrous ethanol, and dried at 40℃ and 12.1kPa for 5 h to obtain MPS-modified graphite; 16g of MPS-modified carbon black and 8g of MPS-modified graphite were mixed to obtain a carbon conductive agent; 2g of KH-560 (γ-glycidyl etheroxypropyltrimethoxysilane) was added to 300g of... In a 95wt% ethanol solution, the mixture was stirred at 300 rpm for 20 min, and 5wt% acetic acid solution was added dropwise to adjust the pH to 4. The mixture was stirred at 500 rpm for 20 min, and 28 g of flake silver powder (D50 of 1 μm, aspect ratio of 30:1) and 42 g of spherical silver powder (D50 of 100 nm) were added. The mixture was ultrasonically dispersed at 500 W for 40 min, stirred at 600 rpm for 2 h, filtered, washed three times with anhydrous ethanol, and dried at 40℃ and 10 kPa for 8 h to obtain the silver conductive agent.

[0028] Mix 10g MMA (methyl methacrylate), 10g EGBE (ethylene glycol monobutyl ether), and 0.01g AIBN (azobisisobutyronitrile), stir at 300rpm for 5min, add 7g carbon conductive agent, stir at 2500rpm for 20min, and let stand at 30kPa for 40min to degas, obtaining a base carbon paste. Apply the base carbon paste to the surface of a tantalum core using screen printing. Place the tantalum core in an oven, heat to 70℃ and hold for 30min, then heat to 165℃ and hold for 35min. Remove the tantalum core and cool to room temperature to obtain a base carbon layer. Mix 6g MMA and 7g EGBE, stir at 300rpm for 5min, add 4g polyethylene glycol-1500, 0.01g AIBN, 0.02g p-toluenesulfonic acid, and 0.5g... MPS hydrolysate was stirred at 300 rpm for 10 min, then 6 g of carbon conductive agent was added, and the mixture was stirred at 2500 rpm for 20 min. The mixture was then allowed to stand at 30 kPa for 40 min to degas, yielding a porous carbon paste. This paste was then screen-printed onto a substrate carbon layer. A tantalum core was placed in a vacuum drying oven, heated to 70℃ and held for 30 min, then heated to 120℃ and held for 1 h. Nitrogen gas was introduced, and the temperature was adjusted to 230℃ and the pressure to 5 Pa, maintained for 1 h. The tantalum core was then removed and cooled to room temperature, resulting in a porous carbon layer on the substrate carbon layer. 15 g of bisphenol A epoxy resin and 5 g of MTHP (methyltetrahydrophthalic anhydride) were mixed and stirred at 300 rpm for 10 min. 0.2 g of EMI-24 (2-ethyl-4-methylimidazole) and 6 g of... EGBE (ethylene glycol monobutyl ether) was stirred at 500 rpm for 30 min, 85 g of silver conductive agent was added, and the mixture was stirred at 2500 rpm for 20 min. The mixture was then placed in a 30 kPa environment and allowed to stand for 40 min to remove bubbles, resulting in a silver paste. The silver paste was then coated onto a porous carbon layer using a screen printing process. The mixture was allowed to stand for 45 min, then heated to 70℃ and held for 40 min, and finally heated to 120℃ and held for 2 h, resulting in a silver layer on the porous carbon layer, thus obtaining a composite coating.

[0029] Example 2:

[0030] In this embodiment, 9g of MPS was added to 300g of 95wt% ethanol solution, stirred at 300rpm for 10min, and the pH was adjusted to 5 by adding 10wt% acetic acid solution dropwise. The mixture was stirred at 300rpm for 3.5h to obtain MPS hydrolysate. 18g of carbon black with a particle size of 30nm was added to 100g of 30wt% nitric acid solution, ultrasonically dispersed at 300W for 25min, filtered, washed with deionized water until the eluent was neutral, washed twice with anhydrous ethanol, added to 150g of MPS hydrolysate, stirred at 3200rpm for 10min, stirred at 600rpm for 3h, filtered, washed twice with deionized water, washed twice with anhydrous ethanol, and dried at 40℃ and 12.1kPa for 5h to obtain MPS modified carbon black. 9g of graphite with a particle size of 2μm was added to 100g of... In a 30wt% nitric acid solution, the mixture was ultrasonically dispersed at 300W for 35 min, filtered, washed with deionized water until the eluent was neutral, washed twice with anhydrous ethanol, added to 90g of MPS hydrolysate, stirred at 3200rpm for 10 min, then stirred at 600rpm for 3 h, filtered, washed twice with deionized water, washed twice with anhydrous ethanol, and dried at 40℃ and 12.1kPa for 5 h to obtain MPS-modified graphite; 16g of MPS-modified carbon black and 8g of MPS-modified graphite were mixed to obtain a carbon conductive agent; 2.5g of... KH-560 was added to 310g of 96wt% ethanol solution and stirred at 300rpm for 20min. 5wt% acetic acid solution was added dropwise to adjust the pH to 5. The mixture was stirred at 500rpm for 25min. 29g of flake silver powder (D50 of 1μm, aspect ratio of 30:1) and 40g of spherical silver powder (D50 of 100nm) were added. The mixture was ultrasonically dispersed at 500W for 40min and stirred at 600rpm for 2.5h. The mixture was filtered, washed three times with anhydrous ethanol, and dried at 40℃ and 10kPa for 8h to obtain the silver conductive agent.

[0031] Mix 10g MMA, 11g EGBE, and 0.02g AIBN, stir at 300rpm for 5min, add 9g carbon conductive agent, stir at 2500rpm for 20min, and let stand at 30kPa for 40min to degas, obtaining a base carbon paste. Apply the base carbon paste to the surface of a tantalum core using screen printing. Place the tantalum core in an oven, heat to 65℃ and hold for 40min, then heat to 165℃ and hold for 40min. Remove the tantalum core and cool to room temperature to obtain a base carbon layer. Mix 8g MMA and 10g EGBE, stir at 300rpm for 5min, add 7g polyethylene glycol-1500, 0.02g AIBN, 0.03g p-toluenesulfonic acid, and 1g... MPS hydrolysate was stirred at 300 rpm for 10 min, 7 g of carbon conductive agent was added, and the mixture was stirred at 2500 rpm for 20 min. The mixture was then allowed to stand at 30 kPa for 40 min to degas, yielding a porous carbon paste. This paste was then screen-printed onto a substrate carbon layer. A tantalum core was placed in a vacuum drying oven, heated to 75℃ and held for 35 min, then heated to 125℃ and held for 2 h. Nitrogen gas was introduced, and the temperature was adjusted to 230℃ and the pressure to 5 Pa, maintained for 1 h. The tantalum core was then removed and cooled to room temperature, resulting in a porous carbon layer on the substrate carbon layer. 18 g of bisphenol A epoxy resin and 6 g of MTHP were mixed and stirred at 300 rpm for 10 min. 0.3 g of EMI-24 and 8 g of... EGBE was stirred at 500 rpm for 30 min, 86 g of silver conductive agent was added, and the mixture was stirred at 2500 rpm for 20 min. The mixture was then placed in a 30 kPa environment and allowed to stand for 40 min to remove bubbles, resulting in a silver paste. The silver paste was then coated onto a porous carbon layer using a screen printing process. The mixture was allowed to stand for 45 min, then heated to 75℃ and held for 45 min, and finally heated to 130℃ and held for 2 h, resulting in a silver layer on the porous carbon layer, thus obtaining a composite coating.

[0032] Example 3:

[0033] In this embodiment, 10g of MPS was added to 305g of 95.5wt% ethanol solution, stirred at 300rpm for 10min, and the pH was adjusted to 4.5 by adding 10wt% acetic acid solution dropwise. The mixture was stirred at 300rpm for 4h to obtain MPS hydrolysate. 16g of carbon black with a particle size of 30nm was added to 95g of 40wt% nitric acid solution, ultrasonically dispersed at 300W for 30min, filtered, washed with deionized water until the washings were neutral, washed twice with anhydrous ethanol, added to 155g of MPS hydrolysate, stirred at 3200rpm for 10min, stirred at 600rpm for 2.5h, filtered, washed twice with deionized water, washed twice with anhydrous ethanol, and dried at 40℃ and 12.1kPa for 5h to obtain MPS modified carbon black. 11g of graphite with a particle size of 2μm was added to 90g of... In a 40wt% nitric acid solution, the mixture was ultrasonically dispersed at 300W for 40 min, filtered, washed with deionized water until the eluent was neutral, washed twice with anhydrous ethanol, added to 95g of MPS hydrolysate, stirred at 3200rpm for 10 min, then stirred at 600rpm for 2.5 h, filtered, washed twice with deionized water, washed twice with anhydrous ethanol, and dried at 40℃ and 12.1kPa for 5 h to obtain MPS-modified graphite; 17g of MPS-modified carbon black and 9g of MPS-modified graphite were mixed to obtain a carbon conductive agent; 3g of... KH-560 was added to 305g of 95.5wt% ethanol solution and stirred at 300rpm for 20min. 5wt% acetic acid solution was added dropwise to adjust the pH to 4.5. The mixture was stirred at 500rpm for 30min. 29g of flake silver powder (D50 of 1μm, aspect ratio of 30:1) and 40g of spherical silver powder (D50 of 100nm) were added. The mixture was ultrasonically dispersed at 500W for 40min and stirred at 600rpm for 2.5h. The mixture was filtered, washed three times with anhydrous ethanol, and dried at 40℃ and 10kPa for 8h to obtain the silver conductive agent.

[0034] Mix 12g MMA, 12g EGBE, and 0.01g AIBN, stir at 300rpm for 5min, add 8g carbon conductive agent, stir at 2500rpm for 20min, and let stand at 25kPa for 30min to degas, obtaining a base carbon paste. Apply the base carbon paste to the surface of a tantalum core using screen printing. Place the tantalum core in an oven, heat to 75℃ and hold for 35min, then heat to 168℃ and hold for 50min. Remove the tantalum core and cool to room temperature to obtain a base carbon layer. Mix 9g MMA and 12g EGBE, stir at 300rpm for 5min, add 5g polyethylene glycol-1500, 0.01g AIBN, 0.02g p-toluenesulfonic acid, and 0.6g... MPS hydrolysate was stirred at 300 rpm for 10 min, then 8 g of carbon conductive agent was added, and the mixture was stirred at 2500 rpm for 20 min. The mixture was then allowed to stand at 25 kPa for 30 min to degas, yielding a porous carbon paste. This paste was then screen-printed onto a substrate carbon layer. A tantalum core was placed in a vacuum drying oven, heated to 65℃ and held for 50 min, then heated to 130℃ and held for 1 h. Nitrogen gas was introduced, and the temperature was adjusted to 235℃ and the pressure to 7 Pa, maintained for 1.2 h. The tantalum core was then removed and cooled to room temperature, resulting in a porous carbon layer on the substrate carbon layer. 16 g of bisphenol A epoxy resin and 5.4 g of MTHP were mixed and stirred at 300 rpm for 10 min. 0.25 g of EMI-24 and 7 g of [other components] were added. EGBE was stirred at 500 rpm for 30 min, 82 g of silver conductive agent was added, and stirred at 2500 rpm for 20 min. The mixture was then placed in a 28 kPa environment and allowed to stand for 35 min to degas, resulting in a silver paste. The silver paste was then coated onto a porous carbon layer using a screen printing process. The mixture was allowed to stand for 55 min, then heated to 73℃ and held for 40 min, and finally heated to 130℃ and held for 1 h, resulting in a silver layer on the porous carbon layer, thus obtaining a composite coating.

[0035] Example 4:

[0036] In this embodiment, 10g of MPS was added to 305g of 95.5wt% ethanol solution, stirred at 300rpm for 10min, and the pH was adjusted to 4.5 by adding 10wt% acetic acid solution dropwise. The mixture was stirred at 300rpm for 4h to obtain MPS hydrolysate. 16g of carbon black with a particle size of 30nm was added to 95g of 40wt% nitric acid solution, ultrasonically dispersed at 300W for 30min, filtered, washed with deionized water until the washings were neutral, washed twice with anhydrous ethanol, added to 155g of MPS hydrolysate, stirred at 3200rpm for 10min, stirred at 600rpm for 2.5h, filtered, washed twice with deionized water, washed twice with anhydrous ethanol, and dried at 40℃ and 12.1kPa for 5h to obtain MPS modified carbon black. 11g of graphite with a particle size of 2μm was added to 90g of... In a 40wt% nitric acid solution, the mixture was ultrasonically dispersed at 300W for 40 min, filtered, washed with deionized water until the eluent was neutral, washed twice with anhydrous ethanol, added to 95g of MPS hydrolysate, stirred at 3200rpm for 10 min, then stirred at 600rpm for 2.5 h, filtered, washed twice with deionized water, washed twice with anhydrous ethanol, and dried at 40℃ and 12.1kPa for 5 h to obtain MPS-modified graphite; 17g of MPS-modified carbon black and 9g of MPS-modified graphite were mixed to obtain a carbon conductive agent; 2.5g of... KH-560 was added to 310g of 96wt% ethanol solution and stirred at 300rpm for 20min. 5wt% acetic acid solution was added dropwise to adjust the pH to 5. The mixture was stirred at 500rpm for 25min. 30g of flake silver powder (D50 of 1μm, aspect ratio of 30:1) and 44g of spherical silver powder (D50 of 100nm) were added. The mixture was ultrasonically dispersed at 500W for 40min and stirred at 600rpm for 3h. The mixture was filtered, washed three times with anhydrous ethanol, and dried at 40℃ and 10kPa for 8h to obtain the silver conductive agent.

[0037] Mix 9g MMA, 15g EGBE, and 0.02g AIBN, stir at 300rpm for 5min, add 5g carbon conductive agent, stir at 2500rpm for 20min, and let stand at 25kPa for 30min to degas, obtaining a base carbon paste. Apply the base carbon paste to the surface of a tantalum core using screen printing. Place the tantalum core in an oven, heat to 65℃ and hold for 50min, then heat to 168℃ and hold for 45min. Remove the tantalum core and cool to room temperature to obtain a base carbon layer. Mix 5g MMA and 9g EGBE, stir at 300rpm for 5min, add 6g polyethylene glycol-1500, 0.02g AIBN, 0.03g p-toluenesulfonic acid, and 0.8g... MPS hydrolysate was stirred at 300 rpm for 10 min, then 9 g of carbon conductive agent was added, and the mixture was stirred at 2500 rpm for 20 min. The mixture was then allowed to stand at 25 kPa for 30 min to degas, yielding a porous carbon paste. This paste was then screen-printed onto a substrate carbon layer. A tantalum core was placed in a vacuum drying oven, heated to 75℃ and held for 45 min, then heated to 125℃ and held for 1.5 h. Nitrogen gas was introduced, and the temperature was adjusted to 235℃ and the pressure to 7 Pa, maintained for 1.2 h. The tantalum core was then removed and cooled to room temperature, resulting in a porous carbon layer on the substrate carbon layer. 18 g of bisphenol A epoxy resin and 6 g of MTHP were mixed and stirred at 300 rpm for 10 min. 0.3 g of EMI-24 and 8 g of [other components] were added. EGBE was stirred at 500 rpm for 30 min, 86 g of silver conductive agent was added, and the mixture was stirred at 2500 rpm for 20 min. The mixture was then placed in a 30 kPa environment and allowed to stand for 40 min to remove bubbles, resulting in a silver paste. The silver paste was then coated onto a porous carbon layer using a screen printing process. The mixture was allowed to stand for 45 min, then heated to 70℃ and held for 50 min, and finally heated to 120℃ and held for 1 h, resulting in a silver layer on the porous carbon layer, thus obtaining a composite coating.

[0038] Example 5:

[0039] In this embodiment, 11g of MPS was added to 310g of 96wt% ethanol solution, stirred at 300rpm for 10min, and the pH was adjusted to 4 by adding 10wt% acetic acid solution dropwise. The mixture was stirred at 300rpm for 3h to obtain MPS hydrolysate. 20g of carbon black with a particle size of 30nm was added to 110g of 35wt% nitric acid solution, ultrasonically dispersed at 300W for 28min, filtered, washed with deionized water until the washings were neutral, washed twice with anhydrous ethanol, added to 160g of MPS hydrolysate, stirred at 3200rpm for 10min, stirred at 600rpm for 2h, filtered, washed twice with deionized water, washed twice with anhydrous ethanol, and dried at 40℃ and 12.1kPa for 5h to obtain MPS modified carbon black. 12g of graphite with a particle size of 2μm was added to 110g of... In a 35wt% nitric acid solution, the mixture was ultrasonically dispersed at 300W for 37 min, filtered, washed with deionized water until the eluent was neutral, washed twice with anhydrous ethanol, added to 100g of MPS hydrolysate, stirred at 3200rpm for 10 min, then stirred at 600rpm for 2 h, filtered, washed twice with deionized water, washed twice with anhydrous ethanol, and dried at 40℃ and 12.1kPa for 5 h to obtain MPS-modified graphite; 18g of MPS-modified carbon black and 7g of MPS-modified graphite were mixed to obtain a carbon conductive agent; 2g of... KH-560 was added to 300g of 95wt% ethanol solution and stirred at 300rpm for 20min. 5wt% acetic acid solution was added dropwise to adjust the pH to 4.5. The mixture was stirred at 500rpm for 30min. 29g of flake silver powder (D50 of 1μm, aspect ratio of 30:1) and 40g of spherical silver powder (D50 of 100nm) were added. The mixture was ultrasonically dispersed at 500W for 40min and stirred at 600rpm for 2.5h. The mixture was filtered, washed three times with anhydrous ethanol, and dried at 40℃ and 10kPa for 8h to obtain the silver conductive agent.

[0040] Mix 11g MMA, 10g EGBE, and 0.01g AIBN, stir at 300rpm for 5min, add 9g carbon conductive agent, stir at 2500rpm for 20min, and let stand at 28kPa for 35min to degas, obtaining a base carbon paste. Apply the base carbon paste to the surface of a tantalum core using screen printing. Place the tantalum core in an oven, heat to 70℃ and hold for 40min, then heat to 170℃ and hold for 45min. Remove the tantalum core and cool to room temperature to obtain a base carbon layer. Mix 9g MMA and 7g EGBE, stir at 300rpm for 5min, add 6g polyethylene glycol-1500, 0.01g AIBN, 0.02g p-toluenesulfonic acid, and 1g... MPS hydrolysate was stirred at 300 rpm for 10 min, 6 g of carbon conductive agent was added, and the mixture was stirred at 2500 rpm for 20 min. The mixture was then allowed to stand at 28 kPa for 35 min to degas, yielding a porous carbon paste. This paste was then screen-printed onto a substrate carbon layer. A tantalum core was placed in a vacuum drying oven, heated to 70℃ and held for 45 min, then heated to 125℃ and held for 1.5 h. Nitrogen gas was introduced, and the temperature was adjusted to 240℃ and the pressure to 8 Pa, maintained for 1.5 h. The tantalum core was then removed and cooled to room temperature, resulting in a porous carbon layer on the substrate carbon layer. 18 g of bisphenol A epoxy resin and 6 g of MTHP were mixed and stirred at 300 rpm for 10 min. 0.3 g of EMI-24 and 7 g of [unspecified ingredient] were added. EGBE was stirred at 500 rpm for 30 min, 82 g of silver conductive agent was added, and stirred at 2500 rpm for 20 min. The mixture was then placed in a 25 kPa environment and allowed to stand for 30 min to degas, resulting in a silver paste. The silver paste was then coated onto a porous carbon layer using a screen printing process. The mixture was allowed to stand for 50 min, then heated to 75℃ and held for 40 min, and finally heated to 125℃ and held for 1.5 h, resulting in a silver layer on the porous carbon layer, thus obtaining a composite coating.

[0041] Example 6:

[0042] In this embodiment, 11g of MPS was added to 310g of 96wt% ethanol solution, stirred at 300rpm for 10min, and the pH was adjusted to 4 by adding 10wt% acetic acid solution dropwise. The mixture was stirred at 300rpm for 3h to obtain MPS hydrolysate. 20g of carbon black with a particle size of 30nm was added to 110g of 35wt% nitric acid solution, ultrasonically dispersed at 300W for 28min, filtered, washed with deionized water until the washings were neutral, washed twice with anhydrous ethanol, added to 160g of MPS hydrolysate, stirred at 3200rpm for 10min, stirred at 600rpm for 2h, filtered, washed twice with deionized water, washed twice with anhydrous ethanol, and dried at 40℃ and 12.1kPa for 5h to obtain MPS modified carbon black. 12g of graphite with a particle size of 2μm was added to 110g of... In a 35wt% nitric acid solution, the mixture was ultrasonically dispersed at 300W for 37 min, filtered, washed with deionized water until the eluent was neutral, washed twice with anhydrous ethanol, added to 100g of MPS hydrolysate, stirred at 3200rpm for 10 min, then stirred at 600rpm for 2 h, filtered, washed twice with deionized water, washed twice with anhydrous ethanol, and dried at 40℃ and 12.1kPa for 5 h to obtain MPS-modified graphite; 18g of MPS-modified carbon black and 7g of MPS-modified graphite were mixed to obtain a carbon conductive agent; 2g of... KH-560 was added to 300g of 95wt% ethanol solution and stirred at 300rpm for 20min. 5wt% acetic acid solution was added dropwise to adjust the pH to 4.5. The mixture was stirred at 500rpm for 30min. 29g of flake silver powder (D50 of 1μm, aspect ratio of 30:1) and 40g of spherical silver powder (D50 of 100nm) were added. The mixture was ultrasonically dispersed at 500W for 40min and stirred at 600rpm for 2.5h. The mixture was filtered, washed three times with anhydrous ethanol, and dried at 40℃ and 10kPa for 8h to obtain the silver conductive agent.

[0043] Mix 11g MMA, 10g EGBE, and 0.01g AIBN, stir at 300rpm for 5min, add 9g carbon conductive agent, stir at 2500rpm for 20min, and let stand at 28kPa for 35min to degas, obtaining a base carbon paste. Apply the base carbon paste to the surface of a tantalum core using screen printing. Place the tantalum core in an oven, heat to 70℃ and hold for 40min, then heat to 170℃ and hold for 45min. Remove the tantalum core and cool to room temperature to obtain a base carbon layer. Mix 9g MMA and 7g EGBE, stir at 300rpm for 5min, add 6g polyethylene glycol-1500 and 0.01g AIBN... AIBN was stirred at 300 rpm for 10 min, then 6 g of carbon conductive agent was added and stirred at 2500 rpm for 20 min. The mixture was then allowed to stand at 28 kPa for 35 min to degas, yielding a porous carbon paste. This paste was then screen-printed onto a substrate carbon layer. A tantalum core was placed in a vacuum drying oven, heated to 70℃ and held for 45 min, then heated to 125℃ and held for 1.5 h. Nitrogen gas was introduced, and the temperature was adjusted to 240℃ and the pressure to 8 Pa, maintained for 1.5 h. The tantalum core was then removed and cooled to room temperature, resulting in a porous carbon layer on the substrate carbon layer. 18 g of bisphenol A epoxy resin and 6 g of MTHP were mixed and stirred at 300 rpm for 10 min, then 0.3 g of... EMI-24 and 7g EGBE were stirred at 500rpm for 30min. 82g silver conductive agent was added and stirred at 2500rpm for 20min. The mixture was then placed in a 25kPa environment and allowed to stand for 30min to degas, resulting in a silver paste. The silver paste was then coated onto a porous carbon layer using a screen printing process. The mixture was allowed to stand for 50min, then heated to 75℃ and held for 40min. Finally, it was heated to 125℃ and held for 1.5h to obtain a silver layer on the porous carbon layer, thus obtaining a composite coating.

[0044] The present invention also includes comparative examples and related experiments.

[0045] Comparative Example 1:

[0046] The difference between this comparative example and Example 5 is that polyethylene glycol-1500 was not added to the pore-forming carbon slurry. The other operating conditions and steps are the same as in Example 5, and a composite coating is obtained.

[0047] Comparative Example 2:

[0048] The difference between this comparative example and Example 5 is that, in the preparation of the pore-forming carbon slurry, the carbon black and graphite in the carbon conductive agent were not treated with MPS hydrolysate. The remaining operating conditions and steps were the same as in Example 5, resulting in a composite coating.

[0049] Comparative Example 3:

[0050] A graphite layer and a silver layer are obtained according to the method disclosed in Chinese patent application document CN108962421A, and the graphite layer and the silver layer constitute a composite coating.

[0051] ESR value and insulation resistance value test

[0052] Tantalum cores with composite coatings on the surfaces of each embodiment and comparative example were encapsulated in plastic to prepare tantalum capacitors. Each tantalum capacitor was connected to a Kelvin fixture and placed in a constant temperature environment of 25°C. A positive polarization voltage of 100kHz and 2.2V was continuously applied. The power supply was disconnected on days 1, 5, 15, 30, and 50. The ESR value (mΩ) of each tantalum capacitor was measured using an LCR meter, and the insulation resistance value (GΩ) of each tantalum capacitor was measured using a high resistance meter. The results are shown in Table 1.

[0053] Table 1

[0054]

[0055] As shown in Table 1, compared with Example 6, the tantalum capacitors prepared in Examples 1 to 5 had lower ESR values ​​and higher insulation resistance values ​​after 50 days of use. This indicates that adding MPS hydrolysate and p-toluenesulfonic acid to the pore-forming carbon paste is beneficial to improving the mechanical strength of the composite coating, maintaining the structural integrity of the composite coating during long-term use, and improving the long-term stability of the tantalum capacitor. Compared with Comparative Example 1, the tantalum capacitor prepared in Example 5 had lower ESR values ​​and higher insulation resistance values, and still maintained good performance after 50 days of use. This indicates that adding polyethylene glycol-1500 to the pore-forming carbon paste can increase the contact area between the silver layer and the carbon layer, reduce the insulation resistance of the composite coating, and improve the long-term stability of the tantalum capacitor. The resistance value of the layer is reduced, thereby lowering the ESR value of the tantalum capacitor. Simultaneously, it prevents the silver layer from debonding from the carbon layer, maintaining the structural integrity of the composite coating during long-term use. Compared to Comparative Example 2, the tantalum capacitor prepared in Example 5 still has a lower ESR value and a higher insulation resistance value after 50 days of use. This indicates that treating carbon black and graphite with MPS hydrolysate effectively improves the mechanical strength of the porous carbon layer, enhances the structural stability of the composite coating, and improves the long-term stability of the tantalum capacitor. Compared to Comparative Example 3, the tantalum capacitor prepared in Example 5 has a lower ESR, indicating that the composite coating prepared in this invention has a lower resistance value, thus reducing the ESR value of the tantalum capacitor.

Claims

1. A method for preparing a composite coating on a tantalum surface, characterized in that, The composite coating comprises a base carbon layer, a porous carbon layer, and a silver layer, and its process includes the following steps: S1. The solvent, MMA, and initiator are mixed, and a carbon conductive agent is added for dispersion. After degassing, a base carbon paste is obtained and coated on the surface of the tantalum core. The paste is then heated and cured to form a base carbon layer. The carbon conductive agent is prepared as follows: carbon black is dispersed in a 30-40 wt% nitric acid solution and reacted for 25-30 min. After washing, it is dispersed in MPS hydrolysate and reacted for 2-3 h. After washing, it is dried under reduced pressure to obtain MPS modified carbon black. Graphite is dispersed in a 30-40 wt% nitric acid solution and reacted for 35-40 min. After washing, it is dispersed in MPS hydrolysate and reacted for 2-3 h. After washing, it is dried under reduced pressure to obtain MPS modified graphite. The MPS modified carbon black and MPS modified graphite are mixed to obtain the carbon conductive agent. The washing liquids are deionized water and anhydrous ethanol. The MPS hydrolysate is prepared as follows: a 95-96 wt% ethanol solution and MPS are mixed, and an acetic acid solution is added dropwise to adjust the pH to 4-5. The mixture is reacted for 3-4 h to obtain the MPS hydrolysate. S2. Mix the solvent, MMA, polyethylene glycol-1500 and initiator, add carbon conductive agent to disperse, degas to obtain pore-forming carbon paste and coat it on the base carbon layer, heat to cure and form pores, forming a porous carbon layer on the base carbon layer. S3. Bisphenol A epoxy resin, curing agent, curing catalyst and solvent are mixed evenly, silver conductive agent is added for dispersion, and after degassing, silver paste is obtained and coated on porous carbon layer. The mixture is heated and cured to form a silver layer on the porous carbon layer, thereby obtaining a composite coating. The silver conductive agent is obtained by modifying silver powder with epoxy silane.

2. The method for preparing a composite coating on a tantalum surface according to claim 1, characterized in that, In step S1, the solvents EGBE, MMA and initiator AIBN are mixed, and a carbon conductive agent is added for dispersion. The mixture is placed in a 25-30 kPa environment and allowed to stand for 30-40 minutes to degas, resulting in a base carbon paste. This paste is then coated onto the surface of the tantalum core. The temperature is raised to 65-75℃ and held for 30-50 minutes, then raised to 165℃-170℃ and held for 35-50 minutes. Finally, the mixture is cooled to obtain the base carbon layer.

3. The method for preparing a composite coating on a tantalum surface according to claim 1, characterized in that, In step S2, the solvents EGBE, MMA, polyethylene glycol-1500 and initiator AIBN are mixed, and a carbon conductive agent is added for dispersion. The mixture is then placed in a 25-30 kPa environment for static degassing for 30-40 min to obtain a porous carbon slurry, which is then coated onto the substrate carbon layer. The mixture is heated to 65-75℃ and held for 30-50 min, then heated to 120-130℃ and held for 1-2 h. The mixture is then placed in a nitrogen atmosphere and maintained at 230-240℃ and 5-8 Pa for 1-1.5 h. After cooling, a porous carbon layer is obtained on the substrate carbon layer.

4. The method for preparing a composite coating on a tantalum surface according to claim 3, characterized in that, In step S2, MPS hydrolysate and p-toluenesulfonic acid are also added during mixing.

5. The method for preparing a composite coating on a tantalum surface according to claim 1, characterized in that, The silver conductive agent is prepared by mixing KH-560 with 95-96wt% ethanol solution, adding acetic acid solution to adjust the pH to 4-5, reacting for 20-30 min, adding silver powder to disperse, reacting for 2-3 h, filtering, washing with anhydrous ethanol, and drying under reduced pressure to obtain the silver conductive agent; the silver powder includes flake silver powder and spherical silver powder.

6. The method for preparing a composite coating on a tantalum surface according to claim 5, characterized in that, In step S3, bisphenol A epoxy resin, curing agent MTHP, curing catalyst EMI-24 and solvent EGBE are mixed evenly, silver conductive agent is added for dispersion, and the mixture is placed in a 25-30 kPa environment for static degassing for 30-40 min to obtain silver paste, which is then coated onto a porous carbon layer. The mixture is left to stand for 45-55 min, heated to 70-75℃ and held for 40-50 min, and then heated to 120-130℃ and held for 1-2 h to form a silver layer on the porous carbon layer, thus obtaining a composite coating.

7. A composite coating on a tantalum surface, characterized in that, The composite coating on the tantalum surface is prepared by the method described in any one of claims 1-6, wherein the base carbon layer comprises the following parts by weight of raw materials: MMA 9-12 parts, EGBE 10-15 parts, carbon conductive agent 5-9 parts, and AIBN 0.01-0.02 parts; the porous carbon layer comprises the following parts by weight of raw materials: MMA 5-9 parts, EGBE 7-12 parts, polyethylene glycol-1500 4-7 parts, AIBN 0.01-0.02 parts, p-toluenesulfonic acid 0-0.03 parts, MPS hydrolysate 0-1 parts, and carbon conductive agent 6-9 parts; and the silver layer comprises the following parts by weight of raw materials: bisphenol A epoxy resin 15-18 parts, MTHP 5-6 parts, EMI-24 0.2-0.3 parts, EGBE 6-8 parts, and silver conductive agent 82-86 parts. The MPS hydrolysate comprises the following raw materials in parts by weight: 300-310 parts of 95-96 wt% ethanol solution and 9-11 parts of MPS.

8. The composite coating on a tantalum surface according to claim 7, characterized in that, The carbon conductive agent comprises 16-18 parts by weight of MPS modified carbon black and 7-9 parts by weight of MPS modified graphite. The MPS-modified carbon black comprises the following raw materials in parts by weight: 16-20 parts carbon black and 150-160 parts MPS hydrolysate; the MPS-modified graphite comprises the following raw materials in parts by weight: 9-12 parts graphite and 90-100 parts MPS hydrolysate; the silver conductive agent comprises the following raw materials in parts by weight: 2-3 parts KH-560, 300-310 parts 95-96wt% ethanol solution, 28-30 parts flake silver powder, and 40-44 parts spherical silver powder.

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