Aluminum powder sintered foil and method for manufacturing the same, aluminum electrolytic capacitor

Abstract

This invention discloses a method for preparing sintered aluminum powder foil, the obtained sintered aluminum powder foil, and an aluminum electrolytic capacitor. The method for preparing the sintered aluminum powder foil includes the following steps: mixing aluminum powder, a complex, an organic solvent, and a binder uniformly to obtain a slurry, wherein the complex is formed by the combination of carboxylic acid and boric acid; coating the slurry onto the surface of a substrate and drying it to obtain a semi-finished product; sintering the semi-finished product under a protective gas atmosphere, and then annealing it at a lower temperature to obtain the desired sintered aluminum powder foil. In this method for preparing sintered aluminum powder foil, during the sintering process, the complex decomposes and releases carboxylic acid and boric acid. The acidic substances coating the surface of the aluminum powder are enhanced by high temperature, which can effectively react with the oxide film on the surface of the aluminum powder, remove the oxide layer on the surface of the aluminum powder, and make effective contact between the aluminum powder particles. During sintering under a protective gas atmosphere, it is easier to form a sintering neck, thus improving the bending performance of the final sintered aluminum powder foil. After high-temperature sintering, the temperature is lowered and annealed to 400 degrees Celsius. Air is introduced to react with the residual carbon in the sintered foil, thereby reducing the residual carbon in the sintered foil and thus reducing the leakage current of the sintered foil.

Description

Technical Field

[0001] This invention relates to the field of sintered foil technology, and in particular to an aluminum powder sintered foil and its preparation method, and an aluminum electrolytic capacitor. Background Technology

[0002] Currently, aluminum electrolytic capacitors are widely used in the energy field due to their characteristics. For example, they are used in small electronic devices such as mobile phones, household appliances such as cameras, inverter power supplies for hybrid vehicles, and energy storage in wind power generation. Thus, aluminum electrolytic capacitors are used for various applications, requiring voltages corresponding to their uses and exhibiting high capacitance. Existing aluminum electrolytic capacitors use anode and cathode foils that are formed on the aluminum foil surface through chemical etching or electrochemical DC / AC etching in strong acid solutions, creating sponge-like pores (low-voltage foil) or tunnel-like pores (high-voltage foil) in the aluminum foil surface. The etching process dissolves and removes excess aluminum from the aluminum foil surface to form a complex porous structure, which is a subtractive manufacturing process. The etched aluminum metal enters the acid solution, resulting in a large amount of waste acid containing high concentrations of aluminum ions, which has a negative impact on the environment. Furthermore, the porous structure formed by etching has a small specific surface area, often resulting in insufficient specific capacitance per unit area. How to form a well-connected porous structure with a high specific surface area on the aluminum foil surface is a key technical element for preparing high-specific-capacitance aluminum electrolytic capacitor electrode materials.

[0003] Patent CN201880052949 discloses an aluminum electrolytic capacitor using aluminum foil with fine aluminum powder attached to its surface. Patent CN201480004009 discloses an electrolytic capacitor using an electrode foil on one or both sides of a smooth aluminum foil with a foil thickness of 15 μm or more but less than 35 μm. This electrode foil contains aggregates of microparticles of similar aluminum in the scale range of 2 μm to 0.01 μm and / or aluminum with an aluminum oxide layer formed on its surface. However, the methods disclosed in the above documents for attaching aluminum powder to aluminum foil by plating and / or vapor deposition are not sufficient, at least for applications involving medium to high voltage capacitors. Furthermore, as an electrode material for aluminum electrolytic capacitors, patent CN202280012314 discloses an electrode material for aluminum electrolytic capacitors composed of at least one sintered body of aluminum and aluminum alloys. This sintered body has a unique structure formed by sintering a laminated body in which aluminum or aluminum alloy powder particles are stacked while maintaining inter-particle voids. Therefore, it is possible to obtain a capacitance equal to or greater than that of existing etched foils. The capacitance of this electrode material can be increased by increasing the amount or thickness of the laminated powder. However, when the thickness of the above-mentioned electrode material is increased to improve its capacitance, there is a problem that it is difficult to form an anodic oxide film (dielectric) on the electrode surface during the chemical forming process. Therefore, as long as the capacitance per unit amount (thickness) of the laminate can be increased, the electrode material can be made thinner. For example, if the capacitance per laminate thickness is increased by 10%, the thickness of the electrode material can be reduced by 9% relative to the core material, which can make the capacitor smaller. In addition, the raw material aluminum powder can be obtained by classifying atomized powder (powder obtained by blowing nitrogen or the like onto a fine stream of molten aluminum at high speed to disperse it and then cooling it). The average particle size (D50) of the powder used to achieve high capacitance in the graded powder is 2 to 6 μm. Even if powder with a large average particle size is used, it is difficult to achieve the desired capacitance. On the other hand, in the case of manufacturing by atomization, powder with a small average particle size accounts for less than 50% of the total weight, and the handling of powder with a large average particle size becomes a problem. Regardless of the average particle size of the aluminum powder used, as long as a high-capacity electrode material is obtained, the yield of atomized powder is greatly improved and the manufacturing cost is reduced. Thus, it is desirable to develop a manufacturing method that can produce high-capacity electrode materials regardless of the average particle size of the aluminum powder.

[0004] In summary, the current aluminum powder sintered foil has the following problems:

[0005] 1) Due to the dense natural oxide film on the surface of aluminum powder, this film acts as a barrier to the fusion of the aluminum powder during the sintering process, resulting in insufficient sintering strength between the aluminum powder particles. This manifests as poor bending performance of the sintered foil, making it prone to breakage and powder shedding. This hinders the subsequent chemical formation of the sintered foil and its winding into a capacitor core.

[0006] 2) In the sintering foil manufacturing process, aluminum powder, organic solvent, and binder are first dispersed into a slurry in a certain proportion, then coated onto both sides of the aluminum foil substrate. After drying, a well-adhesive aluminum powder coating is formed, which is then sintered in a high-temperature inert atmosphere. The binder's role is to ensure good adhesion of the aluminum powder to the substrate, forming a coating of uniform thickness. For the next sintering step, the binder must completely decompose and vaporize at high temperature, leaving no residue in the sintered layer. However, since the sintering of aluminum powder is completed under high vacuum and an inert atmosphere, the residual carbon formed by the high-temperature decomposition of the binder in this atmosphere will coat the surface of the aluminum powder and cannot be completely decomposed into gas and released. Due to the conductive properties of carbon, the residual carbon on the aluminum powder surface will cause trace amounts of residual carbon to be embedded in the alumina layer of the aluminum powder after chemical formation of the sintered body, resulting in increased leakage current in the subsequently manufactured capacitors. Summary of the Invention

[0007] Therefore, it is necessary to provide a method for preparing aluminum powder sintered foil that can solve the above problems.

[0008] In addition, it is necessary to provide an aluminum powder sintered foil prepared by the above preparation method and an aluminum electrolytic capacitor.

[0009] A method for preparing aluminum powder sintered foil includes the following steps:

[0010] Aluminum powder, complex, organic solvent and binder are mixed evenly to obtain a slurry, wherein the complex is formed by the combination of carboxylic acid and boric acid;

[0011] The slurry is coated onto the surface of a substrate and dried to obtain a semi-finished product, which includes a substrate and an aluminum powder coating on the surface of the substrate.

[0012] The semi-finished product is sintered in a protective gas atmosphere and then cooled and annealed to obtain the desired aluminum powder sintered foil.

[0013] In one embodiment, the carboxylic acid is selected from at least one of oxalic acid, salicylic acid, malic acid, and citric acid.

[0014] In one embodiment, the complex is selected from at least one of bis(oxalato)boronic acid, bis(salicylate)boronic acid, citrate-boronic acid, and malate-boronic acid;

[0015] The complex is bis(oxalato)boronic acid, and the molar ratio of oxalic acid to boric acid is 1.8~2.2:1;

[0016] The complex is bis(salicylic acid)boronic acid, and the molar ratio of salicylic acid to boric acid is 1.8~2.2:1.

[0017] In one embodiment, during the operation of uniformly mixing aluminum powder, complex, organic solvent and binder, the mass ratio of aluminum powder, complex, organic solvent and binder is 50~70:0.1~0.5:30~50:0.5~2.

[0018] In one embodiment, the operation of obtaining the desired aluminum powder sintered foil after cooling annealing is as follows: the temperature of the semi-finished product is reduced to 350℃~450℃, an oxidizing atmosphere is introduced into the protective gas atmosphere, and the temperature is maintained for 1 h~24 h to allow the residual carbon in the semi-finished product to react with oxygen to generate carbon dioxide, and then the temperature is further reduced to room temperature to obtain the aluminum powder sintered foil.

[0019] In one embodiment, the organic solvent is selected from at least one of butyl acetate, ethanol, toluene, and ethyl acetate;

[0020] The adhesive is selected from at least one of ethyl cellulose, polyvinyl butyral, polyacrylic acid resin or polycarbonate resin;

[0021] The substrate is high-purity aluminum foil (bright foil) or high-purity aluminum foil (etched foil);

[0022] The protective gas atmosphere is selected from at least one of nitrogen atmosphere, helium atmosphere, neon atmosphere, argon atmosphere, krypton atmosphere and xenon atmosphere.

[0023] In one embodiment, during the sintering of the semi-finished product in a protective gas atmosphere, the sintering temperature is 560°C to 660°C, and the sintering time is 4 hours to 24 hours.

[0024] In one embodiment, the method for preparing the aluminum powder sintered foil further includes, after obtaining the semi-finished product through drying and before sintering the semi-finished product under a protective gas atmosphere, performing the following operation: rolling the semi-finished product to reduce the thickness of the aluminum powder coating by 10% to 15%;

[0025] The method for preparing the aluminum powder sintered foil further includes, after obtaining the desired aluminum powder sintered foil through cooling annealing, performing anodizing treatment on the aluminum powder sintered foil.

[0026] An aluminum powder sintered foil is prepared by the above-described method for preparing aluminum powder sintered foil.

[0027] An aluminum electrolytic capacitor comprising the aforementioned sintered aluminum powder foil.

[0028] The method for preparing this aluminum powder sintered foil of the present invention involves uniformly mixing aluminum powder, a complex, an organic solvent, and a binder to obtain a slurry. The complex is formed by the combination of carboxylic acid and boric acid. During the process of forming an aluminum powder coating after the slurry dries, the organic solvent evaporates, and the complex forms a coating layer on the surface of the aluminum powder and exists in the binder. During the subsequent sintering process, the complex decomposes and releases carboxylic acid and boric acid. The acidic substances coating the surface of the aluminum powder become more acidic under high temperature, which can effectively react with the oxide film on the surface of the aluminum powder, remove the oxide layer on the surface of the aluminum powder, and make effective contact between the aluminum powder particles. When sintering in a protective gas atmosphere, it is easier to form a sintering neck, thereby increasing the bonding force between aluminum powder particles and between aluminum powder and the substrate, and improving the bending performance of the final aluminum powder sintered foil.

[0029] Furthermore, during the subsequent sintering process, the carboxylic acid and boric acid released by the decomposition of the complex can act as catalysts during the high-temperature pyrolysis of the polymer, thereby promoting the decomposition of the binder into gaseous substances at high temperatures, reducing the final residual carbon rate, and solving the problem of high leakage current caused by high residual carbon content from the source.

[0030] Based on the test examples, the aluminum powder sintered foil prepared by the method of the present invention has better bending performance, and compared with the traditional aluminum powder sintered foil, it solves the problem of high leakage current caused by high residual carbon content.

[0031] Preferably, the operation of obtaining the desired aluminum powder sintered foil after cooling annealing is as follows: the temperature of the semi-finished product is reduced to 350℃~450℃, an oxidizing atmosphere is introduced into the protective gas atmosphere, and the temperature is maintained for 1 h~24 h to allow the residual carbon in the semi-finished product to react with oxygen to generate carbon dioxide, and then the temperature is further reduced to room temperature to obtain the aluminum powder sintered foil.

[0032] By sintering in a protective gas atmosphere, strong sintering necks are formed between aluminum powders and between aluminum powders and the substrate, which greatly improves the bonding strength. Introducing an oxidizing atmosphere during annealing no longer affects the sintering strength between aluminum powders and between aluminum powders and the substrate. The oxygen in the introduced oxidizing atmosphere can react effectively with residual carbon at this temperature to generate gaseous carbon dioxide, thereby further reducing the residual carbon content on the surface of the aluminum powder. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating a method for preparing aluminum powder sintered foil according to one embodiment. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Combination Figure 1 This invention discloses a method for preparing aluminum powder sintered foil according to one embodiment, comprising the following steps:

[0036] S10. Mix aluminum powder, complex, organic solvent and binder evenly to obtain slurry. The complex is formed by the combination of carboxylic acid and boric acid.

[0037] Preferably, in this embodiment, the carboxylic acid is selected from at least one of oxalic acid, salicylic acid, malic acid, and citric acid.

[0038] Boric acid is insoluble in organic solvents, while the complex formed by carboxylic acid and boric acid is soluble in organic solvents, thereby improving its dispersibility. At the same time, the complex can also be fully mixed with adhesives.

[0039] Preferably, the complex is selected from at least one of bis(oxalato)boronic acid, bis(salicylic)boronic acid, citrate-boronic acid, and malate-boronic acid.

[0040] Specifically, the complex can be bis(oxalate-boric acid) with a molar ratio of oxalic acid to boric acid of 1.8 to 2.2:1; the complex can also be bis(salicylic acid-boric acid) with a molar ratio of salicylic acid to boric acid of 1.8 to 2.2:1.

[0041] Dioxalate-boric acid can be prepared as follows: 2 mol of oxalic acid and 1 mol of boric acid are added to 200 g of pure water and heated until completely dissolved. Then, the water is removed by vacuum rotary distillation, and the remaining dry powder is dried in an oven at 120 degrees Celsius for 1 hour to obtain the finished product.

[0042] Preferably, in this embodiment, during the process of uniformly mixing aluminum powder, complex, organic solvent and binder, the mass ratio of aluminum powder, complex, organic solvent and binder is 50~70:0.1~0.5:30~50:0.5~2.

[0043] Preferably, in this embodiment, the organic solvent is selected from at least one of butyl acetate, ethanol, toluene, and ethyl acetate.

[0044] Preferably, in this embodiment, the binder is selected from at least one of ethyl cellulose, polyvinyl butyral, polyacrylate resin and polycarbonate resin.

[0045] Generally speaking, aluminum powder can be purchased directly.

[0046] Specifically, in this embodiment, the aluminum powder can be aluminum powder with a D10 value of 1.4μm, a D50 value of 2.5μm, and a D90 value of 4.0μm.

[0047] S20. The slurry is coated on the surface of the substrate and dried to obtain a semi-finished product. The semi-finished product includes the substrate and the aluminum powder coating on the surface of the substrate.

[0048] During the process of forming an aluminum powder coating after the slurry dries, the organic solvent evaporates, the complex forms a coating layer on the surface of the aluminum powder, and exists in the binder.

[0049] The process of applying a slurry to the surface of a substrate can be accomplished using a coating machine. Generally, the slurry is applied to both sides of the substrate.

[0050] In S20, drying can be performed using conventional drying methods. For example, drying can be carried out at 80℃~150℃ for 1min~10min.

[0051] In S20, the specific thickness of the formed aluminum powder coating can be set according to actual needs. For example, the thickness of the aluminum powder coating can be 20μm~100μm.

[0052] Preferably, in this embodiment, the substrate is selected from at least one of high-purity aluminum foil (bright foil) and high-purity aluminum foil (etched foil).

[0053] The specific thickness of the substrate can be set according to actual needs. For example, the thickness of the substrate can be 10μm to 100μm.

[0054] S30. The semi-finished product is sintered in a protective gas atmosphere, and then cooled and annealed to obtain the required aluminum powder sintered foil.

[0055] During the sintering process of the semi-finished product under a protective gas atmosphere, the complex decomposes and releases carboxylic acid and boric acid. The acidic substances coating the surface of the aluminum powder become more acidic under high temperature, which can effectively react with the oxide film on the surface of the aluminum powder, remove the oxide layer on the surface of the aluminum powder, and make effective contact between the aluminum powders. When sintering under a protective gas atmosphere, it is easier to form sintering necks, thereby increasing the bonding force between aluminum powders and between aluminum powder and the substrate, and improving the bending performance of the final aluminum powder sintered foil.

[0056] In addition, during the sintering of the semi-finished product in a protective gas atmosphere, the carboxylic acid and boric acid released by the decomposition of the complex can act as catalysts during the high-temperature pyrolysis of the polymer, thereby promoting the decomposition of the binder into gaseous substances at high temperatures, reducing the final residual carbon rate, and solving the problem of high leakage current caused by high residual carbon content from the source.

[0057] Preferably, in this embodiment, the method for preparing aluminum powder sintered foil further includes, after obtaining a semi-finished product through drying, and before sintering the semi-finished product in a protective gas atmosphere, performing the following operation: rolling the semi-finished product to reduce the thickness of the aluminum powder coating by 10% to 15%.

[0058] Roll forming can be completed directly through roll forming equipment.

[0059] Preferably, in this embodiment, the protective gas atmosphere is selected from at least one of nitrogen atmosphere, helium atmosphere, neon atmosphere, argon atmosphere, krypton atmosphere and xenon atmosphere.

[0060] Preferably, in this embodiment, during the sintering of the semi-finished product under a protective gas atmosphere, the sintering temperature is 560℃~660℃ and the sintering time is 4h~12h.

[0061] Preferably, in this embodiment, the operation of obtaining the desired aluminum powder sintered foil after cooling annealing is as follows: the temperature of the semi-finished product is reduced to 350℃~450℃, an oxidizing atmosphere is introduced into the protective gas atmosphere, and the temperature is maintained for 1 h~24 h to allow the residual carbon in the semi-finished product to react with oxygen to generate carbon dioxide, and then the temperature is further reduced to room temperature to obtain the aluminum powder sintered foil.

[0062] Generally, the oxidizing atmosphere can be an oxygen atmosphere or an air atmosphere, and the specific amount of oxidizing atmosphere added can be determined according to the actual situation.

[0063] For example, the flow rate of the introduced air atmosphere can be from 1L / min to 30L / min.

[0064] Preferably, the operation of obtaining the desired aluminum powder sintered foil after cooling annealing is as follows: the temperature of the semi-finished product is reduced to 350℃~450℃, an oxidizing atmosphere is introduced into the protective gas atmosphere, and the temperature is maintained for 1 h~24 h to allow the residual carbon in the semi-finished product to react with oxygen to generate carbon dioxide, and then the temperature is further reduced to room temperature to obtain the aluminum powder sintered foil.

[0065] By sintering in a protective gas atmosphere, strong sintering necks are formed between aluminum powders and between aluminum powders and the substrate, which greatly improves the bonding strength. Introducing an oxidizing atmosphere during annealing no longer affects the sintering strength between aluminum powders and between aluminum powders and the substrate. The oxygen in the introduced oxidizing atmosphere can react effectively with residual carbon at this temperature to generate gaseous carbon dioxide, thereby further reducing the residual carbon content on the surface of the aluminum powder.

[0066] Preferably, in this embodiment, the method for preparing aluminum powder sintered foil further includes anodizing the aluminum powder sintered foil after obtaining the desired aluminum powder sintered foil through cooling annealing.

[0067] The method for preparing this aluminum powder sintered foil of the present invention involves uniformly mixing aluminum powder, a complex, an organic solvent, and a binder to obtain a slurry. The complex is formed by the combination of carboxylic acid and boric acid. During the process of forming an aluminum powder coating after the slurry dries, the organic solvent evaporates, and the complex forms a coating layer on the surface of the aluminum powder and exists in the binder. During the subsequent sintering process, the complex decomposes and releases carboxylic acid and boric acid. The acidic substances coating the surface of the aluminum powder become more acidic under high temperature, which can effectively react with the oxide film on the surface of the aluminum powder, remove the oxide layer on the surface of the aluminum powder, and make effective contact between the aluminum powder particles. When sintering in a protective gas atmosphere, it is easier to form a sintering neck, thereby increasing the bonding force between aluminum powder particles and between aluminum powder and the substrate, and improving the bending performance of the final aluminum powder sintered foil.

[0068] Furthermore, during the subsequent sintering process, the carboxylic acid and boric acid released by the decomposition of the complex can act as catalysts during the high-temperature pyrolysis of the polymer, thereby promoting the decomposition of the binder into gaseous substances at high temperatures, reducing the final residual carbon rate, and solving the problem of high leakage current caused by high residual carbon content from the source.

[0069] Based on the test examples, the aluminum powder sintered foil prepared by the method of the present invention has better bending performance, and compared with the traditional aluminum powder sintered foil, it solves the problem of high leakage current caused by high residual carbon content.

[0070] The present invention also discloses an embodiment of an aluminum powder sintered foil prepared by the above-described method for preparing aluminum powder sintered foil.

[0071] This aluminum powder sintered foil has better bending performance and, compared with traditional aluminum powder sintered foil, solves the problem of high leakage current caused by high residual carbon content.

[0072] The present invention also discloses an embodiment of an aluminum electrolytic capacitor comprising the above-described aluminum powder sintered foil.

[0073] The following are specific examples.

[0074] In a specific embodiment, the aluminum powder was high-purity spherical aluminum powder purchased from Henan Yuanyang Company, with D50 being 2-3μm; the ethyl cellulose was a chemical reagent purchased from Aladdin Company, of analytical grade; the butyl acetate was a chemical reagent purchased from Aladdin Company, of analytical grade; and the KH-570 was a chemical reagent purchased from Aladdin Company, of analytical grade.

[0075] Preparation of bis(oxalic acid) and boric acid

[0076] Take 2 mol of oxalic acid and 1 mol of boric acid and add them to 200 g of pure water, then heat until completely dissolved. Then remove the water by vacuum rotary distillation. Take out the remaining dry powder and dry it in an oven at 120 degrees Celsius for 1 hour to obtain dioxaloboric acid for later use.

[0077] Example 1

[0078] 1 g of ethyl cellulose binder resin was added to 40 g of butyl acetate as a solvent to prepare a binder resin solution. 0.2 g of the self-prepared bis(oxalato)boronic acid, the binder resin solution, and 60 g of high-purity aluminum powder (purity >99.98%, particle size distribution with D10 value of 1.4 μm, D50 value of 2.5 μm, and D90 value of 4.0 μm) were mixed and dispersed at high speed to prepare a paste composition, which is the slurry. The dispersion effect was judged using a scraper fineness meter, and the fineness was less than 5 μm.

[0079] The prepared slurry was applied to both sides of an aluminum foil (99.99% by weight of aluminum) with a thickness of 30 μm using a comma coater, so that it adhered to both sides of the aluminum foil with a dry film thickness of 60 μm. Then, it was dried at 100°C for 1.5 minutes to allow the slurry layer to dry and form an aluminum powder coating, thus obtaining a semi-finished product.

[0080] The semi-finished product is further rolled using a rolling mill, and pressure is applied to reduce the thickness of the aluminum powder coating by 10%.

[0081] The rolled semi-finished product is heated at 615°C for 5 hours in an argon atmosphere to form a sintered body on the aluminum foil substrate. Then the temperature is reduced to 400°C while air is introduced at a flow rate of 15L / min. The temperature is maintained for 2 hours to allow the residual carbon in the semi-finished product to react with oxygen to generate carbon dioxide. Then the temperature is further reduced to room temperature to obtain the semi-finished aluminum powder sintered foil.

[0082] The manufactured aluminum powder sintered foil was subjected to anodizing treatment to obtain aluminum powder sintered foil. The anodizing treatment was carried out in accordance with the Japan Electronics Manufacturers Association standard RC 2364A, under the condition of a formation voltage of 520 V.

[0083] Example 2

[0084] 1 g of ethyl cellulose binder resin was added to 40 g of butyl acetate as a solvent to prepare a binder resin solution. 0.5 g of the self-prepared bis(oxalato)boronic acid, the binder resin solution, and 60 g of high-purity aluminum powder (purity >99.98%, particle size distribution with D10 value of 1.4 μm, D50 value of 2.5 μm, and D90 value of 4.0 μm) were mixed and dispersed at high speed to prepare a paste composition, which is the slurry. The dispersion effect was judged using a scraper fineness meter, and the fineness was less than 5 μm.

[0085] The prepared slurry was applied to both sides of an aluminum foil (99.99% by weight of aluminum) with a thickness of 30 μm using a comma coater, so that it adhered to both sides of the aluminum foil with a dry film thickness of 60 μm. Then, it was dried at 100°C for 1.5 minutes to allow the slurry layer to dry and form an aluminum powder coating, thus obtaining a semi-finished product.

[0086] The semi-finished product is further rolled using a rolling mill, and pressure is applied to reduce the thickness of the aluminum powder coating by 10%.

[0087] The rolled semi-finished product is heated at 615°C for 5 hours in an argon atmosphere to form a sintered body on the aluminum foil substrate. Then the temperature is reduced to 400°C while air is introduced at a flow rate of 15L / min. The temperature is maintained for 2 hours to allow the residual carbon in the semi-finished product to react with oxygen to generate carbon dioxide. Then the temperature is further reduced to room temperature to obtain the semi-finished aluminum powder sintered foil.

[0088] The manufactured aluminum powder sintered foil was subjected to anodizing treatment to obtain aluminum powder sintered foil. The anodizing treatment was carried out in accordance with the Japan Electronics Manufacturers Association standard RC 2364A, under the condition of a formation voltage of 520 V.

[0089] Example 3

[0090] 1 g of ethyl cellulose binder resin was added to 40 g of butyl acetate as a solvent to prepare a binder resin solution. 0.1 g of the self-prepared bis(oxalato)boronic acid, the binder resin solution, and 60 g of aluminum powder (purity >99.98%, with a particle size distribution of D10 value of 1.4 μm, D50 value of 2.5 μm, and D90 value of 4.0 μm) were mixed and dispersed at high speed to prepare a paste composition, which is the slurry. The dispersion effect was judged using a scraper fineness meter, and the fineness was less than 5 μm.

[0091] The prepared slurry was applied to both sides of an aluminum foil (99.99% by weight of aluminum) with a thickness of 30 μm using a comma coater, so that it adhered to both sides of the aluminum foil with a dry film thickness of 60 μm. Then, it was dried at 100°C for 1.5 minutes to allow the slurry layer to dry and form an aluminum powder coating, thus obtaining a semi-finished product.

[0092] The semi-finished product is further rolled using a rolling mill, and pressure is applied to reduce the thickness of the aluminum powder coating by 10%.

[0093] The rolled semi-finished product is heated at 615°C for 5 hours in an argon atmosphere to form a sintered body on the aluminum foil substrate. Then the temperature is reduced to 400°C while air is introduced at a flow rate of 15L / min. The temperature is maintained for 2 hours to allow the residual carbon in the semi-finished product to react with oxygen to generate carbon dioxide. Then the temperature is further reduced to room temperature to obtain the semi-finished aluminum powder sintered foil.

[0094] The manufactured aluminum powder sintered foil was subjected to anodizing treatment to obtain aluminum powder sintered foil. The anodizing treatment was carried out in accordance with the Japan Electronics Manufacturers Association standard RC 2364A, under the condition of a formation voltage of 520 V.

[0095] Comparative Example 1

[0096] Comparative Example 1 is basically the same as Example 1, except that bis(oxalate)boronic acid was not added to the slurry of Comparative Example 1.

[0097] Comparative Example 2

[0098] Comparative Example 2 is basically the same as Example 1, except that after the aluminum foil in Comparative Example 2 is sintered at 615 degrees, it is still kept in an argon atmosphere during the annealing process at 400 degrees and no air is introduced.

[0099] Test case

[0100] The aluminum powder sintered foils prepared in Examples 1-3 and Comparative Examples 1 and 2 were cut into 5cm×3cm test pieces. The test pieces were then subjected to bending, stretching, capacity and leakage current tests. The test results are shown in Table 1 below.

[0101] Bending and tensile tests were conducted according to the MIT-type automatic bending test method (EIAJRC-2364A) specified by the Japan Electronics and Equipment Manufacturers Association. The automatic bending test apparatus used was the device specified in JIS P8115. The number of bends of the test piece was counted as 1 bend of 90°, 2 bends to return to the original shape, 3 bends of 90° in the opposite direction, and 4 bends to return to the original shape.

[0102] Capacitance and leakage current were tested according to EIAJ RC-2364 standard, and the electrostatic capacitance and leakage current of the test piece were measured. The test piece size was 5cm × 3cm.

[0103] Table 1

[0104]

[0105] Referring to Table 1, it can be seen that the addition of different proportions of acidic complexes in Examples 1-3 significantly affected the flexural strength, and the specific volume also differed significantly due to the effect of the acidic substances. In Comparative Example 1, because no acidic complexes were added to the slurry, the flexural strength of the sintered foil decreased significantly. In Comparative Example 2, the cooling annealing process did not use an oxidizing atmosphere, resulting in a higher residual carbon content in the product and a significant increase in leakage current.

[0106] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0107] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0108] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0109] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method of producing an aluminum powder sintered foil, characterized by, Includes the following steps: Aluminum powder, complex, organic solvent and binder are mixed evenly to obtain a slurry. The complex is formed by the combination of carboxylic acid and boric acid. The complex formed by carboxylic acid and boric acid can be dissolved in organic solvent, thereby improving its dispersibility. At the same time, the complex can also be fully mixed with the binder. The slurry is coated on the surface of a substrate and dried to obtain a semi-finished product. The semi-finished product includes a substrate and an aluminum powder coating coated on the surface of the substrate. During the process of forming the aluminum powder coating after the slurry dries, the organic solvent evaporates, the complex forms a coating layer on the surface of the aluminum powder, and exists in the binder. The semi-finished product is sintered in a protective gas atmosphere and then cooled and annealed to obtain the desired aluminum powder sintered foil.

2. The method for preparing aluminum powder sintered foil according to claim 1, characterized in that, The carboxylic acid is selected from at least one of oxalic acid, salicylic acid, malic acid, and citric acid.

3. The method for preparing aluminum powder sintered foil according to claim 2, characterized in that, The complex is selected from at least one of bis(oxalato)boronic acid, bis(salicylic acid)boronic acid, citrate-boronic acid, and malate-boronic acid. The complex is bis(oxalato)boronic acid, and the molar ratio of oxalic acid to boric acid is 1.8~2.2:1; The complex is bis(salicylic acid)boronic acid, and the molar ratio of salicylic acid to boric acid is 1.8~2.2:

1.

4. The method for preparing aluminum powder sintered foil according to any one of claims 1 to 3, characterized in that, In the operation of uniformly mixing aluminum powder, complex, organic solvent and binder, the mass ratio of aluminum powder, complex, organic solvent and binder is 50~70:0.1~0.5:30~50:0.5~2.

5. The method for preparing aluminum powder sintered foil according to claim 4, characterized in that, The process of obtaining the desired aluminum powder sintered foil after cooling and annealing is as follows: the temperature of the semi-finished product is reduced to 350℃~450℃, an oxidizing atmosphere is introduced into the protective gas atmosphere, and the temperature is maintained for 1 h~24 h to allow the residual carbon in the semi-finished product to react with oxygen to generate carbon dioxide. Then, the temperature is further reduced to room temperature to obtain the aluminum powder sintered foil.

6. The method for preparing aluminum powder sintered foil according to claim 5, characterized in that, The organic solvent is selected from at least one of butyl acetate, ethanol, toluene, and ethyl acetate; The adhesive is selected from at least one of ethyl cellulose, polyvinyl butyral, polyacrylic acid resin or polycarbonate resin; The substrate is high-purity aluminum foil (bright foil) or high-purity aluminum foil (etched foil); The protective gas atmosphere is selected from at least one of nitrogen atmosphere, helium atmosphere, neon atmosphere, argon atmosphere, krypton atmosphere and xenon atmosphere.

7. The method for preparing aluminum powder sintered foil according to claim 5, characterized in that, In the operation of sintering the semi-finished product under a protective gas atmosphere, the sintering temperature is 560℃~660℃ and the sintering time is 4h~24h.

8. The method for preparing aluminum powder sintered foil according to claim 7, characterized in that, The method for preparing the aluminum powder sintered foil further includes, after obtaining the semi-finished product through drying and before sintering the semi-finished product under a protective gas atmosphere, performing the following operation: rolling the semi-finished product to reduce the thickness of the aluminum powder coating by 10% to 15%; The method for preparing the aluminum powder sintered foil further includes, after obtaining the desired aluminum powder sintered foil through cooling annealing, performing anodizing treatment on the aluminum powder sintered foil.

9. A sintered aluminum powder foil, characterized in that, It is prepared by the method for preparing aluminum powder sintered foil according to any one of claims 1 to 8.

10. An aluminum electrolytic capacitor, characterized in that, Includes the aluminum powder sintered foil as described in claim 9.

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