Process for improving anodization consistency of anode foil for aluminum electrolytic capacitor

Abstract

The application discloses a process for improving anodic oxidation consistency of an anode foil for an aluminum electrolytic capacitor, and relates to the technical field of capacitor manufacturing. The process comprises the steps of multi-stage water washing, etching, power feeding, multi-stage formation, intermediate treatment, first post-treatment, baking, second post-treatment, stability treatment, drying, winding, inspection and packaging. The multi-stage formation adopts three-stage oxidation of low-temperature low-current, medium-temperature medium-current and low-temperature high-current, so that the oxidation film forms a base layer, a growth layer and a high-density protective layer, and the layers are uniformly superimposed. Through dynamic water washing, air drying and temperature field and fluid field regulation and control technologies, the consistency and density of the oxidation film are improved. The first post-treatment is used to repair the oxidation film, reduce the pore size of the oxidation film and increase the density of the oxidation film. In combination with high-temperature baking and the second post-treatment step, the oxidation film forms a stable, high-hardness and compact alumina crystal structure, and the water resistance and reliability of the finished anode foil are enhanced.

Description

Technical Field

[0001] The present invention relates to the technical field of capacitor manufacturing, and in particular to a process for improving the anodic oxidation consistency of anode foil for aluminum electrolytic capacitors. Background Art

[0002] Aluminum electrolytic capacitors are widely used in consumer electronics, power management, automotive electronics, industrial control, and other fields due to their high specific capacitance, excellent voltage resistance, and cost advantages. Anode foil, as a core component, has a direct impact on the performance, reliability, and lifespan of the capacitor.

[0003] During the production process of aluminum electrolytic capacitors, the anode foil is usually anodized to form an oxide film with high dielectric strength on its surface. The quality of this oxide film (including thickness uniformity, density, etc.) plays a key role in the leakage current, withstand voltage characteristics and stability of the capacitor. However, in actual mass production, after the anode foil is treated with the existing traditional anodizing process, the consistency of the surface oxide film thickness of the anode foil obtained is difficult to effectively control, resulting in large fluctuations in the uniformity of the anode foil oxide film thickness, causing large fluctuations in the electrical performance of the capacitor, resulting in problems such as reduced yield of aluminum electrolytic capacitors and poor capacitance stability.

[0004] Traditional anodizing processes primarily improve anode foil performance by adjusting the electrolyte formulation or controlling current density. For example, a specific chemical formation process, including pretreatment, primary chemical formation, and phosphoric acid treatment, is employed to form a uniform oxide film on the aluminum foil surface. However, these methods struggle to ensure uniform oxide film thickness on continuous production lines, and their low production stability leads to significant fluctuations in capacitor performance, making them difficult to scale up for large-scale production.

[0005] To address these issues, researchers have attempted various improvements. For example, a sintering process, in which aluminum powder slurry is coated on an aluminum foil substrate and sintered at high temperature to form a three-dimensional porous anode foil, followed by an anodizing process, has improved the specific capacity and mechanical properties of the anode foil to a certain extent. However, in large-scale industrial production, the combination of sintering and anodizing processes has limitations such as complexity and high costs. This has led to the loss of the cost advantage that has made aluminum electrolytic capacitors so widely used, and has become inconsistent with actual production practices.

[0006] With the growing market demand for high-performance, long-life capacitors, the development of efficient, stable, and low-cost anodizing processes has become an urgent need in the industry. Therefore, researching a process that can improve the consistency of anodizing of anode foil for aluminum electrolytic capacitors has important practical significance and broad application prospects.

[0007] In summary, it is found that the existing technology has at least the following technical problems:

[0008] The existing anodizing film forming process has technical problems such as low thickness uniformity and low continuous production stability of the anodized film of the anode foil in large-scale production. Summary of the Invention

[0009] The purpose of the present invention is to provide a process for improving the consistency of anodizing of anode foil for aluminum electrolytic capacitors, so as to solve the technical problems of low thickness uniformity and low continuous production stability of the anodized film of the anode foil in mass production in the existing anodizing film forming process.

[0010] The various technical effects that can be produced by the preferred technical solutions among the various technical solutions provided by the present invention are described in detail below.

[0011] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0012] The present invention provides a process for improving the anodizing consistency of anode foil for aluminum electrolytic capacitors, comprising the following steps: S1, multi-stage water washing: using high-purity aluminum foil, washing it with an acidic or alkaline solution, neutralizing and washing it with a neutralizer, washing it with deionized water with multiple stages of heating, and finally drying it with low-temperature drying air to form a clean aluminum foil;

[0013] S2, etching: chemically etching the clean aluminum foil to form a low-pressure etching foil;

[0014] S3, power feeding: the low-voltage corrosion foil is energized via a conductive roller, and a conductive liquid is sprayed in a high-pressure atomized manner at the dynamic contact point between the conductive roller and the low-voltage corrosion foil;

[0015] S4, multi-stage formation: first, the first stage is formed at low temperature and low current, then the second stage is formed at medium temperature and medium current, and finally the third stage is formed at low temperature and high current; through the three-stage formation, a multi-layered oxide film is formed on the surface of the low-pressure corrosion foil to form a primary anode foil; dynamic water washing and air drying are required between the three stages;

[0016] During the detection, the temperature distribution and flow of the electrolyte in the electrolytic cell are measured by setting a temperature sensor and a fluid flow direction sensor, and the temperature field and fluid field of the electrolyte are analyzed. The air pump gas unit and the propeller convection unit are set to stir and drive the electrolyte flow, so that the various components of the electrolyte are evenly mixed, the temperature field in the electrolytic cell is uniform, and the flow rate in the fluid field is uniform.

[0017] S5, intermediate treatment: chemically treating the primary anode foil with a phosphoric acid solution to form a water-resistant composite oxide film, thereby forming an intermediate-treated anode foil;

[0018] S6, first post-treatment: performing medium-temperature high-current anodic oxidation on the intermediate-treated anode foil to repair the composite oxide film on the surface of the intermediate-treated anode foil and increase the density of the composite oxide film to form a first anode foil;

[0019] S7, calcination treatment: performing high-temperature treatment on the first anode foil to convert the crystals of the composite oxide film into α-Al2O3 type, thereby increasing the density of the composite oxide film and forming a calcined anode foil;

[0020] S8, second post-treatment: chemically treating the baked anode foil with a phosphoric acid solution to generate a water-resistant composite oxide film again to form a second anode foil;

[0021] S9, stability treatment: neutralizing and washing the second anode foil with a neutralizer, and washing the second anode foil with deionized water in multiple stages with heated water to form a final treated anode foil;

[0022] S10, drying: drying the final treated anode foil to form a finished anode foil;

[0023] S11, rolling up;

[0024] S12. Inspection and packaging.

[0025] In one embodiment, the multi-stage water washing step of S1 includes:

[0026] S1.1. Deionized water cleaning: Immerse the high-purity aluminum foil in deionized water at a temperature of 50-60°C and apply ultrasonic vibration for 3-5 minutes;

[0027] S1.2. Cleaning with an acidic or alkaline solution: Use 5-10% by mass sulfuric acid or 5-8% by mass sodium hydroxide solution to clean the high-purity aluminum foil at room temperature for 5-8 minutes;

[0028] S1.3, neutralizer washing: using a 3-5% by mass sodium bicarbonate solution or ammonia solution to clean the high-purity aluminum foil at room temperature for at least 3 minutes;

[0029] S1.4, ethanol washing: using a 70-80% volume fraction ethanol solution, soak the high-purity aluminum foil at room temperature for 2-3 minutes;

[0030] S1.5. Low-temperature, dry air drying: In a clean environment, use dry air at a temperature of 25-35° C. and a wind speed of 3-5 m / s to air-dry the high-purity aluminum foil until there is no water mark on the surface, thereby forming a clean aluminum foil.

[0031] In one embodiment, in step S3, a conductive liquid is sprayed between the conductive roller and the low-voltage etching foil to reduce the contact impedance between the low-voltage etching foil and the conductive roller and improve the uniformity of the electrical reception of the low-voltage etching foil.

[0032] In one embodiment, a silver coating is plated on the conductive roller, and the silver coating contacts the low-voltage corrosion foil to reduce the contact impedance between the conductive roller and the low-voltage corrosion foil.

[0033] In one embodiment, the multi-stage formation step of S4 includes:

[0034] S4.1, the first stage of formation: at a formation temperature of 10-15 ° C and a current density of 5-10 mA / cm 2 Under the conditions of , 5-10% by mass maleic acid solution is used as the forming solution, the voltage is increased to 50% of the target voltage, and the constant voltage is maintained for 10-15 minutes;

[0035] S4.2. First dynamic water washing: rinse the low-pressure etching foil after step S4.1 with deionized water at a temperature of 40-50°C for 1-2 minutes;

[0036] S4.3, Second stage formation: at a formation temperature of 60-70°C and a current density of 10-20 mA / cm 2 Under the conditions of , use 10-15% by mass of boric acid solution as the forming solution, increase the voltage to 80% of the target voltage, and maintain constant voltage for 20-25 minutes;

[0037] S4.4. Second dynamic water washing: Rinse the low-pressure etching foil after step S4.3 with deionized water at a temperature of 40-50°C for 1-2 minutes;

[0038] S4.5, the third stage of formation: at a formation temperature of 25-30 ° C and a current density of 20-30 mA / cm 2 Under the conditions of , use 5-10% by mass ammonium dihydrogen phosphate solution as the chemical forming solution, increase the voltage to 100% of the target voltage, and maintain constant voltage for 5-10 minutes;

[0039] S4.6, third dynamic water washing: rinse the primary anode foil after step S4.5 with deionized water at a temperature of 40-50° C. for 1-2 minutes;

[0040] S4.7. Dynamic air drying: In a clean environment, use dry air at a temperature of 25-35° C. to air dry the primary anode foil completed in step S4.6 until there is no water mark on the surface.

[0041] In one embodiment, S5, intermediate treatment: immersing the primary anode foil in a phosphoric acid solution having a mass fraction of 1-3% and treating at room temperature for 1-3 minutes to form a water-resistant composite oxide film to form the intermediate treated anode foil;

[0042] After the intermediate treatment step in S5, it needs to be washed with water;

[0043] S5.1. Water washing: rinse the treated anode foil with deionized water at a temperature of 40-50° C. at a flow rate of 5-8 L / min for 3-5 minutes.

[0044] In one embodiment, S6, first post-treatment: at a formation temperature of 70-80°C and a current density of 15-25 mA / cm 2 Under the conditions of , using a 10-15% by mass boric acid solution as a chemical forming solution, anodizing the treated anode foil, reducing the voltage to 60% of the target voltage, and maintaining the constant voltage for 30-40 minutes to form the first anode foil;

[0045] After the first post-treatment step of S6, it needs to be washed with water;

[0046] S6.1. Water washing: rinse the first anode foil with deionized water at a temperature of 40-50° C. at a flow rate of 5-8 L / min for 3-5 minutes.

[0047] In one embodiment, the roasting step of S7 includes:

[0048] S7.1, pre-firing: placing the first anode foil in a nitrogen atmosphere, heating it to 300-350°C at a heating rate of 1-5°C / min, and holding it for 30-1 hour;

[0049] S7.2, sintering: In the first stage, the first anode foil is placed in an argon atmosphere and heated to 450-500°C at a heating rate of 5-10°C / min, and kept at this temperature for 20-30 minutes;

[0050] In the second stage, the temperature of the first anode foil is increased to 550-600° C. at a heating rate of 2-5° C. / min and kept at this temperature for 10-20 minutes;

[0051] S7.3, cooling down: lowering the temperature of the first anode foil to 200-250°C at a cooling rate of 10-15°C / min in the furnace, and then naturally cooling the first anode foil to room temperature in an air atmosphere outside the furnace to release the residual stress of the first anode foil treated in step S7.2, thereby forming the baked anode foil.

[0052] In one embodiment, S8, second post-treatment: immersing the baked anode foil in a phosphoric acid solution with a mass fraction of 1-3% at room temperature for 1-3 minutes to form the second anode foil.

[0053] In one embodiment, the stability processing step of S9 includes:

[0054] S9.1, Neutralization treatment: Immerse the second anode foil in a 5% by mass sodium hydroxide solution at room temperature and a temperature of 25-30° C. for 3 minutes;

[0055] S9.2. Deionized water cleaning: rinse the second anode foil after step S9.1 with deionized water at a temperature of 50° C. at a flow rate of 8 L / min for 5 minutes to form the final-treated anode foil.

[0056] The beneficial effects of the present invention are as follows:

[0057] The process provided by the present invention for improving the consistency of anodization of anode foil for aluminum electrolytic capacitors addresses the problems of poor uniformity of oxide film thickness and low continuous production stability in existing anodization film-forming processes in mass production, proposes optimization measures, and achieves a significant improvement in the quality of the oxide film of the anode foil.

[0058] First, a multi-stage water washing step (S1) effectively removes impurities from the surface of the high-purity aluminum foil, improving the uniformity of subsequent anodization. Second, in the current feeding step (S3), a high-pressure atomized conductive liquid is sprayed to stabilize the contact between the low-voltage etching foil and the conductive roller, reducing oxide film thickness variations caused by uneven current distribution.

[0059] During the multi-stage formation step S4, a three-stage oxidation process (low temperature, low current, medium temperature, medium current, and low temperature, high current) is used, combined with dynamic water washing and low-temperature air drying to form a multi-layered oxide layer. The oxide film formed by each oxidation formation step is layered, and the uniformity of the oxide film at each location on the primary anode foil is controlled. Each oxidation step requires cleaning to prevent the formation liquid from the previous stage from remaining in the pores of the oxide film, preventing it from affecting the oxidation formation in the next stage. This is conducive to improving the uniformity of the next oxide layer, thereby improving the uniformity of the overall oxide film and effectively improving the structure of the oxide film. After the final dynamic water washing, the oxide film of the primary anode foil is cooled and air-dried to gradually reduce the stress, improving the density and stability of the oxide film.

[0060] At the same time, temperature sensors and fluid flow direction sensors are set up to monitor the temperature field and fluid field in the electrolytic cell, and the air pump aeration unit and propeller convection unit are used to promote the uniform distribution of the electrolyte, ensuring the uniformity of the oxide film generated on the anode foil in a large-scale production environment, making the generation of the oxide film more uniform.

[0061] The subsequent intermediate treatment step S5, the first post-treatment step S6, the roasting treatment step S7, and the second post-treatment step S8, through phosphoric acid solution chemical treatment, secondary anodization and high-temperature roasting, gradually transform the composite oxide film from amorphous (non-crystalline) Al2O3, hydrated alumina film and porous Al2O3 into γ'-Al2O3 in the pre-burning stage of the roasting treatment, and then into γ-Al2O3 type in the first stage of normal firing. Finally, in the second stage of normal firing, α-Al2O3 type crystals with the most compact crystal structure are generated. The residual stress of the first anode foil and the oxide film is gradually reduced during the annealing treatment; thereby significantly improving the water resistance, density and stability of the oxide film, and thus enhancing the reliability of the capacitor.

[0062] After the final stability treatment step S9 and the drying step S10, the residual treatment liquid and substances in the second anode foil after the second post-treatment step S8 are further removed, thereby improving the stability of the oxide film. This reduces the acidic residue on the surface of the oxide film of the second anode foil, reduces the impact on the stability of the solid electrolyte in the capacitor, stabilizes the performance of the capacitor, and ensures that the anode foil has excellent corrosion resistance and consistency during long-term use.

[0063] The process of the present invention not only optimizes the uniformity of oxide film thickness and reduces capacitor performance fluctuations, but also improves the stability and consistency of the production process, thereby increasing the product qualification rate of aluminum electrolytic capacitors, and has important practical value for the large-scale industrial production of aluminum electrolytic capacitors. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for use in the implementation. Obviously, the drawings described below are only some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0065] Figure 1 This is one of the process flow charts of the present invention;

[0066] Figure 2 This is the second process flow chart of the present invention;

[0067] Figure 3 This is a scanning electron microscope image of the microstructure of the oxide film cross section of the first anode foil after step S6 of the present invention;

[0068] Figure 4 This is a scanning electron microscope image of the surface microstructure of the oxide film of the second anode foil after step S8 of the present invention. DETAILED DESCRIPTION

[0069] The technical solutions in the embodiments of the present invention will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present invention.

[0070] In a specific embodiment, a process for improving the consistency of anodizing of anode foil for aluminum electrolytic capacitors is provided, which includes the steps of multi-stage water washing, etching, power feeding, multi-stage chemical formation, intermediate treatment, first post-treatment, roasting, second post-treatment, stability treatment, drying, winding, inspection and packaging. The multi-stage chemical formation adopts a three-stage oxidation of low temperature and low current, medium temperature and medium current, and low temperature and high current, so that the oxide film forms a base layer, a growth layer and a high-density protective layer, which are evenly superimposed layer by layer to improve the specific volume of the anode foil. The uniformity and density of the oxide film are synergistically improved by dynamic water washing, air drying and temperature field and fluid field control technology. The oxide film is repaired by the first post-treatment to reduce the pore size of the oxide film and increase the density of the oxide film. The oxide film is formed into a stable, high-hardness and compact aluminum oxide crystal structure in combination with high-temperature roasting and the second post-treatment step, thereby enhancing the water resistance and reliability of the finished anode foil. The process effectively solves the technical problems of low thickness uniformity and low continuous production stability of the anodized film of the anode foil in mass production in the existing anodizing film forming process.

[0071] The first implementation of a process to improve the consistency of anodizing of anode foil for aluminum electrolytic capacitors Figure 1 As shown, the method comprises the following steps: S1, multi-stage water washing: using high-purity aluminum foil, washing with an acidic or alkaline solution, neutralizing and washing with a neutralizer, washing with deionized water with multiple stages of warm water, and finally drying with low-temperature drying air to form a clean aluminum foil;

[0072] S2, etching: chemically etching the clean aluminum foil to form a low-pressure etching foil;

[0073] S3, power feeding: the low-voltage corrosion foil is energized through the conductive roller, and the conductive liquid is sprayed with high-pressure atomization at the dynamic contact point between the conductive roller and the low-voltage corrosion foil;

[0074] S4, multi-stage formation: First, the first stage is formed at low temperature and low current, then the second stage is formed at medium temperature and medium current, and finally the third stage is formed at low temperature and high current. Through the three-stage formation, a multi-layered oxide film is formed on the surface of the low-voltage corrosion foil to form the primary anode foil. Dynamic water washing and air drying are required between the three stages.

[0075] During the detection, the temperature distribution and flow of the electrolyte in the electrolytic cell are measured by setting a temperature sensor and a fluid flow direction sensor, and the temperature field and fluid field of the electrolyte are analyzed. The air pump gas unit and the propeller convection unit are set to stir and drive the electrolyte flow, so that the various components of the electrolyte are evenly mixed, the temperature field in the electrolytic cell is uniform, and the flow rate in the fluid field is uniform.

[0076] S5, intermediate treatment: chemically treating the primary anode foil with a phosphoric acid solution to form a water-resistant composite oxide film to form an intermediate-treated anode foil;

[0077] S6. First post-treatment: performing medium-temperature, high-current anodization on the intermediate-treated anode foil to repair the composite oxide film on the surface of the intermediate-treated anode foil and increase the density of the composite oxide film to form the first anode foil;

[0078] S7, calcination treatment: performing high temperature treatment on the first anode foil to convert the crystals of the composite oxide film into α-Al2O3 type, thereby increasing the density of the composite oxide film and forming a calcined anode foil;

[0079] S8, second post-treatment: chemically treating the baked anode foil with a phosphoric acid solution to generate a water-resistant composite oxide film again to form a second anode foil;

[0080] S9, stability treatment: neutralizing and washing the second anode foil with a neutralizer, and washing with deionized water in multiple stages with heated water to form a final treated anode foil;

[0081] S10, drying: drying the final treated anode foil to form a finished anode foil;

[0082] S11, rolling up;

[0083] S12. Inspection and packaging.

[0084] During application, in step S1, the high-purity aluminum foil used is a high-purity aluminum foil with an aluminum content of 99.999% and a total amount of impurities ≤10ppm, which is suitable for high-voltage or high-reliability capacitors.

[0085] The low-pressure corrosion foil formed in step S2 has a specific capacitance of 0.8-1.2 μF / cm 2 .

[0086] In step S3, a conductive liquid is sprayed between the conductive roller and the low-voltage etching foil to reduce the contact impedance between the low-voltage etching foil and the conductive roller and improve the uniformity of the low-voltage etching foil receiving electricity.

[0087] In order to improve the conductive effect and reduce the impedance, a silver coating is further plated on the conductive roller, and the silver coating contacts the low-voltage corrosion foil to reduce the contact impedance between the conductive roller and the low-voltage corrosion foil.

[0088] During application, the contact impedance between the low-voltage corrosion foil and the conductive roller is reduced by spraying conductive liquid and silver coating. Without increasing the voltage, the current can be increased to a large extent, avoiding the burning of the low-voltage corrosion foil due to excessive voltage during the formation process. At the same time, it can improve the uniformity of the heating and shrinkage of the electrode foil during the anodizing process, and realize the formation of a highly consistent high dielectric constant oxide film and the toughness of the electrode foil.

[0089] Through the multi-stage formation in step S4 and the first post-treatment in S6, a multi-layer oxide layer is formed in the S4 stage, which includes a hard and highly adhesive base layer with large voids, a growth layer with extremely small pores and extremely high density, and a high-density protective layer with medium pores, relatively hard texture and high density. Finally, the re-anodization in the S6 step is subjected to a densification formation treatment, so that the multi-layer composite and density of the oxide layer are achieved, forming a uniform and dense oxide film, thereby improving the uniformity of the oxide layer of the anode foil, improving the consistency of the anode foil, and increasing the specific capacitance value.

[0090] The multi-stage water washing step S1 effectively removes impurities from the surface of the high-purity aluminum foil, improving the uniformity of subsequent anodization. Secondly, in the current feeding step S3, high-pressure atomization spraying of conductive liquid is used to stabilize the contact between the low-voltage corrosion foil and the conductive roller, reducing oxide film thickness deviations caused by uneven current distribution.

[0091] During the multi-stage formation step S4, a three-stage oxidation process (low temperature, low current, medium temperature, medium current, and low temperature, high current) is used, combined with dynamic water washing and low-temperature air drying to form a multi-layered oxide layer. The oxide film formed by each oxidation formation step is layered, and the uniformity of the oxide film at each location on the primary anode foil is controlled. Each oxidation step requires cleaning to prevent the formation liquid from the previous stage from remaining in the pores of the oxide film, preventing it from affecting the oxidation formation in the next stage. This is conducive to improving the uniformity of the next oxide layer, thereby improving the uniformity of the overall oxide film and effectively improving the structure of the oxide film. After the final dynamic water washing, the oxide film of the primary anode foil is cooled and air-dried to gradually reduce the stress, improving the density and stability of the oxide film.

[0092] At the same time, temperature sensors and fluid flow direction sensors are set up to monitor the temperature field and fluid field in the electrolytic cell, and the air pump aeration unit and propeller convection unit are used to promote the uniform distribution of the electrolyte, ensuring the uniformity of the oxide film generated on the anode foil in a large-scale production environment, making the generation of the oxide film more uniform.

[0093] The subsequent intermediate treatment step S5, the first post-treatment step S6, the roasting treatment step S7, and the second post-treatment step S8, through phosphoric acid solution chemical treatment, secondary anodization and high-temperature roasting, gradually transform the oxide film from amorphous (non-crystalline) Al2O3, hydrated alumina film and porous Al2O3 into γ'-Al2O3 in the pre-burning stage of the roasting treatment, and then into γ-Al2O3 in the first stage of normal firing. Finally, in the second stage of normal firing, α-Al2O3 crystals with the most compact crystal structure are generated. The residual stress of the first anode foil and the oxide film is gradually reduced during the de-burning treatment; thereby significantly improving the water resistance, density and stability of the oxide film, and thus enhancing the reliability of the capacitor.

[0094] After the final stability treatment step S9 and the drying step S10, the residual treatment liquid and substances in the second anode foil after the second post-treatment step S8 are further removed, thereby improving the stability of the oxide film. This reduces the acidic residue on the surface of the oxide film of the second anode foil, reduces the impact on the stability of the solid electrolyte in the capacitor, stabilizes the performance of the capacitor, and ensures that the anode foil has excellent corrosion resistance and consistency during long-term use.

[0095] Therefore, through the process of improving the anodic oxidation consistency of anode foil for aluminum electrolytic capacitors of the present invention, optimization measures are proposed to address the problems of poor oxide film thickness uniformity and low continuous production stability in the existing anodic oxidation film forming process in mass production, thereby achieving a significant improvement in the quality of the oxide film of the anode foil.

[0096] The process of the present invention not only optimizes the uniformity of oxide film thickness, increases specific capacitance, and reduces capacitor performance fluctuations, but also enhances the stability and consistency of the production process, and improves the product qualification rate of aluminum electrolytic capacitors, and has important practical value for the large-scale industrial production of aluminum electrolytic capacitors.

[0097] As one of the optional implementations

[0098] Regarding the specific cleaning steps of the multi-stage water washing in step S1, this embodiment is as follows. Figure 2 As shown, S1.1, deionized water heating cleaning: S1.1, immerse the high-purity aluminum foil in deionized water at a temperature of 50-60°C and apply ultrasonic vibration for continuous cleaning for 3-5 minutes to promote the removal of easily detached impurities on the surface of the aluminum foil, thereby removing easily detached impurities on the high-purity aluminum foil;

[0099] S1.2. Cleaning with an acidic or alkaline solution: Use 5-10% by mass sulfuric acid or 5-8% by mass sodium hydroxide solution to clean the high-purity aluminum foil at room temperature for 5-8 minutes. By using an acidic or alkaline solution to clean the high-purity aluminum foil after treatment in step S1.1, it is possible to remove strongly adherent grease, impurities, and oxides, as well as grease, impurities, and oxide layers that adhere to the surface of the high-purity aluminum and have penetrated shallowly into the surface.

[0100] S1.3. Neutralizer washing: Use a 3-5% by mass sodium bicarbonate solution or ammonia solution to clean the high-purity aluminum foil at room temperature for at least 3 minutes. By washing the high-purity aluminum foil treated in step S1.2 with the sodium bicarbonate solution or ammonia solution, the attached acidic or alkaline solution can be removed and the residual acidic or alkaline substances can be neutralized.

[0101] S1.4, ethanol washing: Use a 70-80% by volume ethanol solution to soak the high-purity aluminum foil at room temperature for 2-3 minutes; by washing the high-purity aluminum foil treated in step S1.3 with the ethanol solution, the neutralizing agent and any residual substances of the neutralizing agent can be washed away;

[0102] S1.5. Low temperature and dry air drying: In a clean environment, use dry air at a temperature of 25-35°C and a wind speed of 3-5m / s to air dry the high-purity aluminum foil until there is no water mark on the surface, forming a clean aluminum foil.

[0103] During application, high-purity aluminum foil will absorb grease, oxides, or form Al2O3 during rolling or storage, which needs to be thoroughly removed by acid and alkali cleaning to avoid insufficient purity of the aluminum foil caused by the introduction of impurities and prevent impurity residues from causing oxide film defects.

[0104] In step S1.5, during air drying, the dry air used is dry air with a relative humidity of 10-20% RH;

[0105] After, drying experiment comparison:

[0106]

[0107] Among them, preferably, dry air with a relative humidity of 20% RH is used, and the drying time is set to at least 6 minutes to control the surface moisture content of the high-purity aluminum foil in an appropriate range to avoid causing static electricity.

[0108] Regarding the specific steps of the multi-stage formation of the above-mentioned step S4, this embodiment is as follows. Figure 2 As shown, S4.1, first stage formation: under the conditions of a formation temperature of 10-15°C and a current density of 5-10 mA / cm2, a 5-10% by mass maleic acid solution is used as the formation liquid, the voltage is increased to 50% of the target voltage, and the constant voltage is maintained for 10-15 minutes; low temperature formation forms a hard and strongly adherent base oxide layer with large gaps as the first layer of the oxide film;

[0109] S4.2. First Dynamic Water Wash: Rinse the low-pressure etched foil after step S4.1 with deionized water at 40-50°C for 1-2 minutes. This first dynamic water wash removes any residual chemical residue from step S4.2 and any oxidized materials that are unstable with the aluminum metal of the low-pressure etched foil.

[0110] S4.3, second stage formation: under the conditions of a formation temperature of 60-70°C and a current density of 10-20mA / cm2, a boric acid solution with a mass fraction of 10-15% is used as a formation liquid, the voltage is increased to 80% of the target voltage, and the constant voltage is maintained for 20-25 minutes; medium temperature and medium current formation forms a growing oxide layer with extremely small pores and extremely high density. Since the growing oxide layer has a high density but low hardness, it adheres to the base oxide layer as the first layer of the oxide film and can be interwoven with the large pores of the base oxide layer, so that the growing oxide layer and the base oxide layer have a tight structure, thereby reducing the amount and shedding rate of oxide on the growing oxide layer in subsequent formation steps.

[0111] S4.4. Second dynamic water wash: Rinse the low-pressure etched foil after step S4.3 with deionized water at 40-50°C for 1-2 minutes. This second dynamic water wash removes any residual formation solution and any oxidizing materials that are unstable with the underlying oxide layer on the surface of the low-pressure etched foil after step S4.3.

[0112] S4.5, Third Formation: Under conditions of a formation temperature of 25-30°C and a current density of 20-30 mA / cm², use a 5-10% by mass ammonium dihydrogen phosphate solution as the formation fluid. Boost the voltage to 100% of the target voltage and maintain constant voltage for 5-10 minutes. This low temperature and high current form a dense protective layer with medium porosity, a hard texture, high density, and strong adhesion. This layer protects the oxides in the growing oxide layer, forming an oxide film with a stable structure, uniform texture, and high consistency.

[0113] S4.6. Third dynamic water wash: Rinse the primary anode foil after step S4.5 with deionized water at 40-50°C for 1-2 minutes. This third dynamic water wash removes any residual formation solution from the low-pressure etching foil surface after step S4.4, as well as any oxidizing materials that are unstable with the growing oxide layer.

[0114] S4.7. Dynamic air drying: In a clean environment, use dry air at a temperature of 25-35°C to air dry the primary anode foil that has completed step S4.6 until there is no trace of water on the surface.

[0115] In the formation steps S4.1, S4.3, and S4.5 above, the target voltage = the rated voltage of the capacitor × the safety margin factor; in steps S4 and S6, the safety margin factor is set to 1.3-1.5.

[0116] During application, the oxide film is grown in a uniform gradient through three stages of formation: low temperature and low current - medium temperature and medium current - low temperature and high current, combined with dynamic water washing between each stage, thereby achieving high-quality growth of the oxide film in the main formation stage.

[0117] Regarding the specific processing steps of the above-mentioned step S5, this embodiment is as follows. Figure 2 As shown, S5, intermediate treatment: immersing the primary anode foil in a phosphoric acid solution with a mass fraction of 1-3%, and treating it at room temperature for 1-3 minutes to form a water-resistant composite oxide film to form an intermediate-treated anode foil;

[0118] After the intermediate treatment step in S5, it needs to be washed with water;

[0119] S5.1. Water washing: Rinse the treated anode foil with deionized water at a temperature of 40-50°C at a flow rate of 5-8 L / min for 3-5 minutes. The water washing in step S5.1 can remove residual substances in the phosphoric acid solution of the treatment, thereby reducing the probability of defects in the oxide film in the subsequent first post-treatment.

[0120] Regarding the specific steps of the first post-processing of the above-mentioned step S6, this embodiment is as follows. Figure 2 As shown, S6, the first post-treatment: at a formation temperature of 70-80 ° C and a current density of 15-25 mA / cm 2 Under the conditions of , using 10-15% by mass boric acid solution as a forming solution, anodizing the treated anode foil, reducing the voltage to 60% of the target voltage, and maintaining the constant voltage for 30-40 minutes to form a first anode foil;

[0121] After the first post-treatment step of S6, it needs to be washed with water;

[0122] S6.1. Water washing: rinse the first anode foil with deionized water at a temperature of 40-50° C. at a flow rate of 5-8 L / min for 3-5 minutes.

[0123] When applying, Figure 3 As shown, the first post-treatment in step S6 can repair the composite oxide film treated in S5, increase the amount of oxide in the oxide film, improve the density of the oxide film, and further improve the specific capacity of the anode foil. At the same time, the bonding degree of the oxide layer in the oxide film is high and the structural stability is good.

[0124] Regarding the specific processing steps of the calcination process in step S7, this embodiment Figure 2 As shown, S7.1, pre-burning: place the first anode foil in a nitrogen atmosphere, increase the temperature to 300-350°C at a heating rate of 1-5°C / min, and keep it at this temperature for 30-1 hour;

[0125] S7.2, Normal Firing: In the first stage, the first anode foil is placed in an argon atmosphere and heated to 450-500°C at a heating rate of 5-10°C / min, and kept at this temperature for 20-30 minutes;

[0126] In the second stage, the temperature of the first anode foil is raised to 550-600°C at a heating rate of 2-5°C / min and kept at this temperature for 10-20 minutes;

[0127] S7.3, cooling down: cool the temperature of the first anode foil to 200-250°C at a cooling rate of 10-15°C / min in the furnace, and then naturally cool the first anode foil to room temperature in the air atmosphere outside the furnace to release the stress of the first anode foil treated in step S7.2, thereby forming a baked anode foil.

[0128] During application, the calcination step S7 causes the crystals of the composite oxide film treated in step S6 to gradually transform from amorphous (non-crystalline) Al2O3, hydrated alumina film and porous Al2O3 in the pre-calcination stage of the calcination process to γ'-Al2O3, and then to γ-Al2O3 in the first stage of the calcination process. Finally, in the second stage of the calcination process, α-Al2O3 crystals with the tightest crystal structure are generated. The residual stress of the first anode foil and the oxide film is gradually reduced during the annealing process, thereby significantly improving the water resistance, density and stability of the oxide film, thereby enhancing the reliability of the capacitor.

[0129] Regarding the specific processing steps of the second post-processing of the above-mentioned step S8, this embodiment is as follows. Figure 2 As shown, S8, second post-treatment: immersing the baked anode foil in a phosphoric acid solution with a mass fraction of 1-3% at room temperature for 1-3 minutes to form a second anode foil.

[0130] During application, after the calcination treatment in step S7, the unstable crystals of the oxide film are converted into stable crystals, which are then further treated with phosphoric acid solution to form a water-resistant composite oxide film that is stable, highly uniform, and highly consistent with the oxide film. Figure 4 As shown in the figure, the amount of aluminum phosphate generated can hinder the migration of oxygen-containing substances (such as water) into the anode, so that porous aluminum hydroxide cannot be generated, thereby improving the water resistance of the oxide film, and ultimately allowing the anode foil to obtain a highly reliable composite oxide film, while also improving the specific capacity and production efficiency of the anode foil.

[0131] Regarding the specific processing steps of the second post-processing of the above-mentioned step S9, this embodiment is as follows. Figure 2 As shown, S9.1, neutralization treatment: immerse the second anode foil in a 5% by mass sodium hydroxide solution at room temperature and a solution temperature of 25-30° C. for 3 minutes; by using a low concentration alkaline solution, the acidic substances remaining on the surface of the second anode foil after the treatment in step S8 are neutralized and washed away, while also avoiding destruction of the aluminum phosphate generated in step S8;

[0132] S9.2. Deionized water cleaning: Rinse the second anode foil after step S9.1 with deionized water at a temperature of 50°C at a flow rate of 8 L / min for 5 minutes to remove residual alkaline neutralization solution to form a final treated anode foil.

[0133] During application, after the final stabilization treatment step S9 and the drying step S10, the residual treatment liquid and substances in the second anode foil after the second post-treatment step S8 are further removed to improve the stability of the oxide film; thereby, the acidic residue on the surface of the oxide film of the second anode foil is reduced, reducing the impact on the stability of the solid electrolyte in the capacitor, stabilizing the performance of the capacitor, and ensuring that the anode foil has excellent corrosion resistance and consistency during long-term use.

[0134] The performance of the anode foil for aluminum electrolytic capacitors prepared by the process for improving the anodic oxidation consistency of the anode foil for aluminum electrolytic capacitors according to the present invention is significantly improved compared to the anode foil prepared by the conventional chemical forming process. The specific performance is shown in Table 1 below. The experiment was conducted using an anode foil having a thickness of 80 μm. The experimental parameters are shown in the table below:

[0135] Forming voltage (V) Withstand voltage (V) <![CDATA[Specific capacitance (μF / cm 2 )]]> 30 31.2 78.22 60 61.8 23.65 90 92.3 8.73

[0136] A second embodiment of the process for improving the anodizing consistency of anode foil for aluminum electrolytic capacitors is different from the first embodiment in that the conductive liquid in step S3 can be: 50-100 g / L sodium sulfate solution or 5-15 g / L phosphoric acid solution, and 0.1-0.5% polyethylene glycol (PEG-400) is added as a wetting agent.

[0137] When spraying, the atomization pressure is 0.2-0.4MPa, the flow rate is 5-8ml / min, and the temperature of the conductive liquid is 25-35℃ to avoid volatilization.

[0138] When used, the conductive roller with a silver coating is in contact with the low-voltage etching foil, which can reduce the impedance of the conductive roller and the low-voltage etching foil, increase the current intensity, and promote the formation of oxides.

[0139] The third embodiment of the process for improving the consistency of anodizing of anode foil for aluminum electrolytic capacitors is different from the first embodiment in that a plurality of temperature sensors and fluid flow direction sensors are provided; wherein, a temperature sensor is provided every 20 cm along the length of the electrolytic cell, and the accuracy of measuring temperature is within ±0.5°C; a fluid flow direction sensor is provided every 30 cm along the length of the electrolytic cell, and is arranged in the vertical direction at one-third of the depth of the electrolyte from top to bottom; a plurality of air pump venting units and propeller convection units are provided; wherein, the air pump venting units are provided along the length of the electrolytic cell. One propeller convection unit is set every 1m in the length direction of the electrolytic cell, and nitrogen is emitted at a flow rate of 0.1-0.3L / min. The bubble diameter is controlled at 1-2mm and is evenly distributed; one propeller convection unit is set at each end of the length direction of the electrolytic cell, and the two propeller convection units are located on different sides of the electrolytic cell, with the jet directions facing each other. The two propeller convection units are set at a height of one-third of the bottom of the electrolytic cell, the rotation speed is controlled at 100-200 revolutions per minute, and the flow rate of the electrolyte is controlled at 0.2-0.5m / s, so that the electrolyte forms a circulation in the cell.

[0140] On the plane, the aluminum foil passes between the two propeller convection units.

[0141] During the multi-stage formation in step S4, each electrolytic cell is provided with a temperature sensor, a fluid flow direction sensor, an air pump unit and a propeller convection unit to stir and drive the electrolyte to flow, so that the components of the electrolyte are evenly mixed, the temperature in the electrolytic cell is uniform, and the flow rate in the fluid field is uniform, thereby promoting the uniformity and consistency of the oxide film formation of the aluminum foil.

[0142] The technical features of the above embodiments may be arbitrarily combined. To simplify the description, not all possible combinations of the technical features in the above embodiments are described.

Claims

1. A process for improving the anodizing consistency of anode foil for aluminum electrolytic capacitors, characterized in that: The following steps are involved: S1. Multi-stage water washing: Use high-purity aluminum foil, wash it with acidic or alkaline solution, neutralize it with a neutralizer, wash it with deionized water with warm water in multiple stages, and finally dry it with low-temperature air to form a clean aluminum foil; S2, etching: chemically etching the clean aluminum foil to form a low-pressure etching foil; S3, power feeding: the low-voltage corrosion foil is energized via a conductive roller, and a conductive liquid is sprayed in a high-pressure atomized manner at the dynamic contact point between the conductive roller and the low-voltage corrosion foil; S4, multi-stage formation: first, the first stage is formed at low temperature and low current, then the second stage is formed at medium temperature and medium current, and finally the third stage is formed at low temperature and high current; through the three-stage formation, a multi-layered oxide film is formed on the surface of the low-pressure corrosion foil to form a primary anode foil; dynamic water washing and air drying are required between the three stages; During the detection, the temperature distribution and flow of the electrolyte in the electrolytic cell are measured by setting a temperature sensor and a fluid flow direction sensor, and the temperature field and fluid field of the electrolyte are analyzed. The air pump gas unit and the propeller convection unit are set to stir and drive the electrolyte flow, so that the various components of the electrolyte are evenly mixed, the temperature field in the electrolytic cell is uniform, and the flow rate in the fluid field is uniform. The multi-stage formation steps of S4 include: S4.1, the first stage of formation: at a formation temperature of 10-15 ° C and a current density of 5-10 mA / cm 2 Under the conditions of , a maleic acid solution with a mass fraction of 5-10% is used as the forming solution, the voltage is increased to 50% of the target voltage, and the constant voltage is maintained for 10-15 minutes; S4.

2. First dynamic water washing: rinse the low-pressure etching foil after step S4.1 with deionized water at a temperature of 40-50°C for 1-2 minutes; S4.3, Second stage formation: at a formation temperature of 60-70°C and a current density of 10-20 mA / cm 2 Under the conditions of , use 10-15% mass fraction of boric acid solution as the forming solution, increase the voltage to 80% of the target voltage, and maintain constant voltage for 20-25 minutes; S4.

4. Second dynamic water washing: Rinse the low-pressure etching foil after step S4.3 with deionized water at a temperature of 40-50°C for 1-2 minutes; S4.5, the third stage of formation: at a formation temperature of 25-30 ° C and a current density of 20-30 mA / cm 2 Under the conditions of , use 5-10% by mass ammonium dihydrogen phosphate solution as the forming solution, increase the voltage to 100% of the target voltage, and maintain constant voltage for 5-10 minutes; S4.6, third dynamic water washing: rinse the primary anode foil after step S4.5 with deionized water at a temperature of 40-50° C. for 1-2 minutes; S4.

7. Dynamic air drying: In a clean environment, use dry air at a temperature of 25-35°C to air dry the primary anode foil obtained in step S4.6 until no trace of water remains on the surface. S5, intermediate treatment: chemically treating the primary anode foil with a phosphoric acid solution to form a water-resistant composite oxide film, thereby forming an intermediate-treated anode foil; S6, first post-treatment: performing medium-temperature high-current anodic oxidation on the intermediate-treated anode foil to repair the composite oxide film on the surface of the intermediate-treated anode foil and increase the density of the composite oxide film to form a first anode foil; S7, calcination treatment: performing high-temperature treatment on the first anode foil to convert the crystals of the composite oxide film into α-Al2O3 type, thereby increasing the density of the composite oxide film and forming a calcined anode foil; S8, second post-treatment: chemically treating the baked anode foil with a phosphoric acid solution to generate a water-resistant composite oxide film again to form a second anode foil; S9, stability treatment: neutralizing and washing the second anode foil with a neutralizer, and washing the second anode foil with deionized water in multiple stages with heated water to form a final treated anode foil; S10, drying: drying the final treated anode foil to form a finished anode foil; S11, rolling up; S12. Inspection and packaging.

2. The process for improving the anodizing consistency of anode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The multi-stage water washing steps of S1 include: S1.

1. Deionized water cleaning: Immerse the high-purity aluminum foil in deionized water at a temperature of 50-60°C and apply ultrasonic vibration for 3-5 minutes; S1.

2. Cleaning with an acidic or alkaline solution: Use 5-10% by mass sulfuric acid or 5-8% by mass sodium hydroxide solution to clean the high-purity aluminum foil at room temperature for 5-8 minutes; S1.3, neutralizer washing: using a 3-5% by mass sodium bicarbonate solution or ammonia solution to clean the high-purity aluminum foil at room temperature for at least 3 minutes; S1.4, ethanol washing: Use 70-80% ethanol solution by volume to soak the high-purity aluminum foil for 2-3 minutes at room temperature; S1.

5. Low-temperature, dry air drying: In a clean environment, use dry air at a temperature of 25-35° C. and a wind speed of 3-5 m / s to air-dry the high-purity aluminum foil until there is no water mark on the surface, thereby forming the clean aluminum foil.

3. The process for improving the anodizing consistency of anode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: In step S3, a conductive liquid is sprayed between the conductive roller and the low-voltage etching foil to reduce the contact impedance between the low-voltage etching foil and the conductive roller and improve the uniformity of the power receiving of the low-voltage etching foil.

4. The process for improving the anodic oxidation consistency of anode foil for aluminum electrolytic capacitors according to claim 3, characterized in that: A silver coating is plated on the conductive roller, and the silver coating contacts the low-voltage corrosion foil to reduce the contact impedance between the conductive roller and the low-voltage corrosion foil.

5. The process for improving the anodizing consistency of anode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: S5, intermediate treatment: immersing the primary anode foil in a phosphoric acid solution with a mass fraction of 1-3%, and treating at room temperature for 1-3 minutes to form a water-resistant composite oxide film to form the intermediate treated anode foil; After the intermediate treatment step in S5, it needs to be washed with water; S5.

1. Water washing: rinse the treated anode foil with deionized water at a temperature of 40-50° C. at a flow rate of 5-8 L / min for 3-5 minutes.

6. The process for improving the anodizing consistency of anode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: S6, first post-treatment: at a formation temperature of 70-80°C and a current density of 15-25 mA / cm 2 Under the conditions of , using a 10-15% by mass boric acid solution as a chemical forming solution, anodizing the treated anode foil, reducing the voltage to 60% of the target voltage, and maintaining the constant voltage for 30-40 minutes to form the first anode foil; After the first post-treatment step of S6, it needs to be washed with water; S6.

1. Water washing: rinse the first anode foil with deionized water at a temperature of 40-50° C. at a flow rate of 5-8 L / min for 3-5 minutes.

7. The process for improving the anodizing consistency of anode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The roasting step of S7 includes: S7.1, pre-firing: placing the first anode foil in a nitrogen atmosphere, heating it to 300-350°C at a heating rate of 1-5°C / min, and holding it for 30-1 hour; S7.2, sintering: In the first stage, the first anode foil is placed in an argon atmosphere and heated to 450-500°C at a heating rate of 5-10°C / min, and kept at this temperature for 20-30 minutes; In the second stage, the temperature of the first anode foil is increased to 550-600° C. at a heating rate of 2-5° C. / min and kept at this temperature for 10-20 minutes; S7.3, cooling down: lowering the temperature of the first anode foil to 200-250°C at a cooling rate of 10-15°C / min in the furnace, and then naturally cooling the first anode foil to room temperature in an air atmosphere outside the furnace to release the residual stress of the first anode foil treated in step S7.2, thereby forming the baked anode foil.

8. The process for improving the anodizing consistency of anode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: S8. Second post-treatment: Immerse the calcined anode foil in a phosphoric acid solution with a mass fraction of 1-3% at room temperature for 1-3 minutes to form the second anode foil.

9. The process for improving the anodizing consistency of anode foil for aluminum electrolytic capacitors according to claim 1, characterized in that: The S9 stabilization process includes: S9.1, Neutralization treatment: Immerse the second anode foil in a 5% by mass sodium hydroxide solution at room temperature and a temperature of 25-30° C. for 3 minutes; S9.

2. Deionized water cleaning: rinse the second anode foil after step S9.1 with deionized water at a temperature of 50° C. at a flow rate of 8 L / min for 5 minutes to form the final-treated anode foil.

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