A method for preparing aluminum capacitor anode foil based on microwave sintering

Abstract

The invention discloses a method for preparing an aluminum capacitor anode foil based on microwave sintering, the method comprising: 1. dispersing nano aluminum powder in ethylene glycol and adding sodium tripolyphosphate solution for ultrasonic dispersion, drying to obtain surface-treated nano aluminum powder; 2. mixing the surface-treated nano aluminum powder with a dispersant, a binder, and a film-forming agent to obtain aluminum paste; 3. coating the aluminum paste on an aluminum foil substrate and drying and curing; 4. microwave sintering to obtain a sintered foil; 5. boiling the sintered foil and drying it; 6. soaking it in a diammonium phosphate solution; 7. chemical treatment to obtain an aluminum capacitor anode foil. The invention adopts a microwave sintering method to complete the sintering process under low-temperature and fast conditions, avoiding the abnormal growth of grains of aluminum powder during long-term, high-temperature sintering, promoting the uniform distribution of aluminum powder in the sintered foil, ensuring the porosity of the sintered foil, thereby improving the capacitance and anti-bending performance of the aluminum capacitor anode foil, and meeting the requirements for use in medium and high voltage environments.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum electrolytic capacitors, and in particular relates to a method for preparing an aluminum capacitor anode foil based on microwave sintering. Background Art

[0002] As a type of electronic component, aluminum electrolytic capacitors are widely used in mobile phones, televisions and other household appliances, as well as power supplies, hybrid power devices and other fields. The traditional aluminum capacitor anode foil uses an etching process to obtain high specific capacitance performance. Subsequently, a part of sintered foils with aluminum powder sintered on the anode foil substrate appeared on the market. Studies have shown that the sintering time in the preparation process of sintered foil is as long as more than 10 hours or even more than 20 hours, and in this process, the electric furnace needs to provide a continuous high-temperature environment. Under the traditional long-term and high-temperature sintering process, not only is the energy consumption high, but the aluminum powder particles in the sintered foil are also very easy to grow, resulting in the clogging of the interconnected gaps between the aluminum powders, the decrease in porosity, and the reduction in the capacitance of the prepared anode foil; at the same time, in the subsequent chemical treatment process of the sintered foil, the aluminum powder particles that are in contact with each other do not have enough space during the surface growth process, which makes the oxide film grow unevenly, and the sample is prone to local "brittleness", thereby affecting the overall anti-bending performance and the subsequent preparation of capacitors. Patents with publication numbers CN112024892A and CN112045190A disclose the flash sintering preparation process and the SPS sintering process respectively. However, the flash sintering process requires the application of a DC auxiliary electric field to cause the flash sintering phenomenon, and the SPS often requires the application of a certain pressure to achieve the densification process of the material itself. Both are difficult to apply in the industrial aluminum foil roll sintering process. Therefore, further research is needed on the low-temperature sintering process of aluminum capacitor sintered foil to meet the needs of industrial production. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method for preparing an aluminum capacitor anode foil based on microwave sintering in view of the deficiencies of the above-mentioned prior art. The method adopts microwave sintering to prepare an aluminum capacitor anode foil, completes the sintering process under low temperature and fast conditions, avoids the abnormal growth of aluminum powder grains during long-term, high-temperature sintering, promotes the uniform distribution of aluminum powder in the sintered foil, and ensures the porosity of the sintered foil, thereby improving the capacitance and anti-bending performance of the aluminum capacitor anode foil, and solves the problem that the aluminum powder particles grow in the traditional sintering process, resulting in a decrease in the capacitance of the anode foil.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for preparing an aluminum capacitor anode foil based on microwave sintering, characterized in that the method comprises the following steps:

[0005] Step 1, dispersing nano aluminum powder in ethylene glycol and adding sodium tripolyphosphate solution, then ultrasonically dispersing at an ultrasonic frequency of 15kHz to 30kHz for 10min to 20min, and then placing in a vacuum drying oven at 80°C to dry, to obtain surface-treated nano aluminum powder;

[0006] Step 2: Evenly mix the surface-treated nano aluminum powder obtained in step 1 with a dispersant, a binder, and a film-forming agent to obtain an aluminum paste;

[0007] Step 3: coating the aluminum paste obtained in step 2 on an aluminum foil substrate, and then placing it in a vacuum drying oven for drying and curing;

[0008] Step 4: placing the aluminum foil cured in step 3 into a microwave sintering furnace, performing microwave sintering in a vacuum environment, and then cooling to room temperature with the furnace to obtain a sintered foil; the microwave sintering temperature is 300° C. to 520° C., the heating time is 10 min to 20 min, and the heat preservation time is 15 min to 30 min;

[0009] Step 5: Boil the sintered foil obtained in step 4 in deionized water for 8 to 15 minutes, and then dry it;

[0010] Step 6: Soak the sintered foil dried in step 5 in a diammonium phosphate solution for 15 to 30 minutes;

[0011] Step 7: Perform chemical treatment on the sintered foil after soaking in step 6 to obtain an aluminum capacitor anode foil.

[0012] The present invention firstly performs surface treatment on the nano aluminum powder, thereby improving the dispersibility of the nano aluminum powder, so that the surface-treated nano aluminum powder is evenly dispersed in the aluminum paste, which is beneficial to improving the dispersion uniformity of the aluminum powder particles in the sintered foil; then the aluminum paste is coated on the aluminum foil substrate, dried, and solidified before microwave sintering; the sintering process is completed under low temperature and fast conditions, thereby avoiding the abnormal growth of the grains of the aluminum powder during the long-term and high-temperature sintering process, which is beneficial to the refinement of the grains, and promoting the uniform distribution of the aluminum powder in the sintered foil, thereby improving the capacitance of the anode foil of the aluminum capacitor; at the same time, the porosity of the sintered foil is guaranteed, and the blockage of the connected pores between the aluminum powders is reduced, so that the sintered foil has enough growth space in the subsequent chemical treatment process, forms a uniform oxide film, avoids the local "embrittlement phenomenon" affecting the anti-bending performance of the anode foil, and meets the requirements for use in medium and high voltage environments.

[0013] The above-mentioned method for preparing an aluminum capacitor anode foil based on microwave sintering is characterized in that the particle size of the nano aluminum powder in step 1 is 40nm~80nm. Since the penetration depth of microwaves into metal materials is limited, the present invention controls the particle size of the nano aluminum powder to be nanometer-level to match and coordinate with the penetration depth of microwaves in the subsequent microwave sintering process, so that the aluminum powder penetrated by the microwave can absorb sufficient microwave energy to heat the aluminum powder, thereby achieving the purpose of microwave sintering.

[0014] The above-mentioned method for preparing an aluminum capacitor anode foil based on microwave sintering is characterized in that the concentration of the sodium tripolyphosphate solution in step 1 is 0.5 mol / L. The present invention controls the concentration of the sodium tripolyphosphate solution to optimize the dispersion stability of the surface-treated nano aluminum powder, thereby ensuring that it can be evenly dispersed in the aluminum paste in the subsequent mixing process.

[0015] The above-mentioned method for preparing an aluminum capacitor anode foil based on microwave sintering is characterized in that the dispersant in step 2 is at least one of triethyl citrate, ethanol, ethylene glycol, pinene alcohol, benzyl alcohol and butyl carbitol acetate, the binder is at least one of ethyl cellulose, PVDF5130, PVA, PVB, PEG-4000 and HSV900, and the film-forming agent is at least one of polyvinyl pyrrolidone, trimethylsiloxysilicate, acrylic resin, dimethylsiloxane, PEG and phenolic resin.

[0016] The above-mentioned method for preparing aluminum capacitor anode foil based on microwave sintering is characterized in that the conductivity of the deionized water in step 5 is σ≤5×10 -4 The present invention controls the conductivity of deionized water to prevent the introduction of impurity ions during the boiling process from affecting the specific capacitance and withstand voltage performance of the product anode foil.

[0017] The above-mentioned method for preparing an aluminum capacitor anode foil based on microwave sintering is characterized in that the concentration of the ammonium dihydrogen phosphate solution in step 6 is 0.3 mol / L. The present invention controls the concentration of the ammonium dihydrogen phosphate solution so that the ammonium dihydrogen phosphate combines with the water and oxide film on the surface of the sintered foil that has been boiled to form a portion of aluminum dihydrogen phosphate, and utilizes the excellent high bending resistance and high compression resistance of aluminum dihydrogen phosphate to improve the bending resistance and compression resistance of the anode foil surface.

[0018] The above-mentioned method for preparing aluminum capacitor anode foil based on microwave sintering is characterized in that the formation voltage used in the formation treatment in step 7 is 530V and the current density is 1.5A / cm 2 ~3A / cm 2, the forming liquid is a boric acid solution system. The present invention ensures the sintering growth thickness of aluminum powder during the forming process by controlling the forming voltage, thereby ensuring the withstand voltage of the aluminum capacitor anode foil, and controls the sintering growth speed of the aluminum powder by controlling the current density, thereby ensuring the quality of the sintering growth of the aluminum powder. By using the boric acid solution system as the forming liquid, the surface tension and conductivity of the forming liquid are improved, and the ionization balance of the forming liquid is changed, thereby improving the withstand voltage of the aluminum capacitor anode foil by more than 5%, and finally making the aluminum capacitor anode foil suitable for high-voltage electrolyte.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] 1. The present invention adopts microwave sintering method to prepare aluminum capacitor anode foil, completes the sintering process under low temperature and fast conditions, avoids the abnormal grain growth of aluminum powder during long-term and high-temperature sintering, promotes the uniform distribution of aluminum powder in the sintered foil, and ensures the porosity of the sintered foil, thereby improving the capacitance and anti-bending performance of the aluminum capacitor anode foil, meeting the requirements for use in medium and high voltage environments.

[0021] 2. The present invention adopts microwave sintering instead of the traditional solid phase sintering process, which improves the performance indicators of the aluminum capacitor anode foil, reduces energy consumption, improves production efficiency, saves time and economic costs, and compared with other rapid sintering processes such as SPS and flash burning, the sintering process of the present invention can achieve the industrial production application conditions of aluminum foil roll sintering.

[0022] 3. The present invention performs surface treatment on nano aluminum powder, thereby improving the dispersibility of nano aluminum powder and solving the problems of agglomeration and uneven dispersion of nano aluminum powder, so that the surface-treated nano aluminum powder is evenly dispersed in the aluminum paste, which is beneficial to improving the dispersion uniformity of aluminum powder particles in the sintered foil, ensuring the uniformity and stability of the sintered foil, and the large specific surface area characteristic of the nano aluminum powder is beneficial to improving the capacitance of the anode foil of the aluminum capacitor.

[0023] 4. The present invention uses ammonium dihydrogen phosphate solution to soak the boiled and dried sintered foil, which promotes the combination of water and oxide film on the surface of the sintered foil to form aluminum dihydrogen phosphate with high bending and high compression resistance, thereby obtaining anode foil for capacitors with high bending performance.

[0024] 5. The present invention adopts a surface treatment process to modify the nano aluminum powder, so that the aluminum powder is easier to disperse in the dispersant to obtain aluminum paste with uniform texture. This process provides an important idea for preparing uniform paste in other fields such as electronic paste, solar front silver paste, and back aluminum paste.

[0025] The technical solution of the present invention is further described in detail below through embodiments. DETAILED DESCRIPTION

[0026] Example 1

[0027] This embodiment includes the following steps:

[0028] Step 1, dispersing nano aluminum powder with a particle size of 40nm~80nm in ethylene glycol and adding a sodium tripolyphosphate solution with a concentration of 0.5mol / L, then ultrasonically dispersing at an ultrasonic frequency of 30kHz for 20min, and then placing in a vacuum drying oven at 80°C to obtain surface-treated nano aluminum powder;

[0029] Step 2, uniformly mixing the surface-treated nano aluminum powder obtained in step 1 with a dispersant, a binder, and a film-forming agent, wherein the mass of the surface-treated nano aluminum powder is 60% of the total mass of the surface-treated nano aluminum powder and the dispersant, the mass of the dispersant is 40% of the total mass of the surface-treated nano aluminum powder and the dispersant, the mass of the binder is 2% of the mass of the dispersant, and the mass of the film-forming agent is 1.5% of the mass of the dispersant, to obtain aluminum paste; the dispersant is triethyl citrate and ethanol, the binder is ethyl cellulose and PVDF5130, and the film-forming agent is polyvinyl pyrrolidone and trimethylsiloxysilicate;

[0030] Step 3: coating the aluminum paste obtained in step 2 on an aluminum foil substrate, and then placing it in a vacuum drying oven for drying and curing at 200° C.;

[0031] Step 4: placing the aluminum foil cured in step 3 into a microwave sintering furnace, performing microwave sintering in a vacuum environment, and then cooling to room temperature with the furnace to obtain a sintered foil; the microwave sintering temperature is 300° C., the heating time is 10 min, and the heat preservation time is 30 min;

[0032] Step 5: Boil the sintered foil obtained in step 4 in deionized water for 15 minutes, and then dry it in a drying oven; the conductivity of the deionized water is σ≤5×10 -4 S / m;

[0033] Step 6: Place the sintered foil dried in step 5 in a 0.3 mol / L diammonium phosphate solution and soak for 30 minutes;

[0034] Step 7: Place the sintered foil soaked in step 6 in a 10% boric acid solution for chemical treatment at a voltage of 530 V and a current density of 1.5 A / cm 2 , and obtain aluminum capacitor anode foil.

[0035] The dispersant in this embodiment can also be replaced by at least one of triethyl citrate, ethanol, ethylene glycol, pinene alcohol, benzyl alcohol and butyl carbitol acetate other than the combination of triethyl citrate and ethanol, the binder can also be replaced by at least one of ethyl cellulose, PVDF5130, PVA, PVB, PEG-4000 and HSV900 other than the combination of ethyl cellulose and PVDF5130, and the film-forming agent can also be replaced by at least one of polyvinyl pyrrolidone, trimethylsiloxysilicate, acrylic resin, dimethylsiloxane, PEG and phenolic resin other than polyvinyl pyrrolidone and trimethylsiloxysilicate.

[0036] Comparative Example 1

[0037] The difference between this comparative example and Example 1 is that the aluminum foil after solidification in step 4 is placed in a vacuum tube furnace and sintered at 250° C. for 3 h, then sintered in a vacuum environment at 570° C. for 5 h, and then cooled to room temperature in the furnace to obtain a sintered foil.

[0038] Example 2

[0039] The difference between this embodiment and embodiment 1 is that the dispersant described in step 2 is pineol and ethylene glycol, the binder is PVB and HSV900, and the film-forming agent is acrylic resin and dimethylsiloxane; the microwave sintering temperature in step 4 is 450°C, the heating time is 15 minutes, and the insulation time is 25 minutes.

[0040] Example 3

[0041] The difference between this embodiment and embodiment 1 is that the dispersant described in step 2 is pineol and benzyl alcohol, the binder is PVB and PEG-4000, and the film-forming agent is phenolic resin and dimethylsiloxane; the microwave sintering temperature in step 4 is 520°C, the heating time is 20 minutes, and the insulation time is 15 minutes.

[0042] Example 4

[0043] The difference between this embodiment and embodiment 1 is that the current density used in the chemical treatment in step 7 is 2A / cm 2 .

[0044] Example 5

[0045] The difference between this embodiment and embodiment 1 is that the current density used in the chemical treatment in step 7 is 3A / cm 2 .

[0046] Example 6

[0047] The difference between this embodiment and embodiment 1 is that the ultrasonic frequency in step 1 is 15 kHz and the ultrasonic dispersion time is 10 min.

[0048] Example 7

[0049] The difference between this embodiment and embodiment 1 is that the boiling time in deionized water in step 5 is 8 minutes.

[0050] Example 8

[0051] The difference between this embodiment and embodiment 1 is that the diammonium phosphate solution soaking time in step 6 is 15 minutes.

[0052] The aluminum capacitor anode foils prepared in Examples 1 to 8 of the present invention and Comparative Example 1 were subjected to an electrostatic capacitance test in an 80 g / L ammonium pentaborate solution, a withstand voltage test in a 70 g / L boric acid solution, and an anti-bending performance test of the aluminum capacitor anode foil after formation was performed using an aluminum foil bending tester. The results are shown in Table 1 below.

[0053] After testing, the electrostatic capacitance of the aluminum capacitor anode foil prepared in Examples 1 to 8 of the present invention is significantly higher than that of the aluminum capacitor anode foil prepared in Comparative Example 1, and the withstand voltage and bending times are comparable, indicating that compared with the traditional vacuum tube furnace sintering, the preparation method using microwave sintering in the present invention significantly improves the specific capacitance performance of the aluminum capacitor anode foil, and at the same time makes the aluminum capacitor anode foil have excellent anti-bending performance.

[0054] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for preparing an aluminum capacitor anode foil based on microwave sintering, characterized in that: The method comprises the following steps: Step 1, dispersing nano aluminum powder in ethylene glycol and adding sodium tripolyphosphate solution, then ultrasonically dispersing at an ultrasonic frequency of 15kHz to 30kHz for 10min to 20min, and then placing in a vacuum drying oven at 80°C to dry, to obtain surface-treated nano aluminum powder; Step 2: Evenly mix the surface-treated nano aluminum powder obtained in step 1 with a dispersant, a binder, and a film-forming agent to obtain an aluminum paste; Step 3: coating the aluminum paste obtained in step 2 on an aluminum foil substrate, and then placing it in a vacuum drying oven for drying and curing; Step 4: placing the aluminum foil cured in step 3 into a microwave sintering furnace, performing microwave sintering in a vacuum environment, and then cooling to room temperature with the furnace to obtain a sintered foil; the microwave sintering temperature is 300° C. to 520° C., the heating time is 10 min to 20 min, and the heat preservation time is 15 min to 30 min; Step 5: Boil the sintered foil obtained in step 4 in deionized water for 8 to 15 minutes, and then dry it; Step 6: Soak the sintered foil dried in step 5 in a diammonium phosphate solution for 15 to 30 minutes; Step 7: Perform chemical treatment on the sintered foil after soaking in step 6 to obtain an aluminum capacitor anode foil.

2. The method for preparing an aluminum capacitor anode foil based on microwave sintering according to claim 1, characterized in that: The particle size of the nano aluminum powder in step 1 is 40nm~80nm.

3. The method for preparing an aluminum capacitor anode foil based on microwave sintering according to claim 1, characterized in that: The concentration of the sodium tripolyphosphate solution in step 1 is 0.5 mol / L.

4. The method for preparing an aluminum capacitor anode foil based on microwave sintering according to claim 1, characterized in that: The dispersant in step 2 is at least one of triethyl citrate, ethanol, ethylene glycol, pinene alcohol, benzyl alcohol and butyl carbitol acetate, the binder is at least one of ethyl cellulose, PVDF5130, PVA, PVB, PEG-4000 and HSV900, and the film-forming agent is at least one of polyvinyl pyrrolidone, trimethylsiloxysilicate, acrylic resin, dimethylsiloxane, PEG and phenolic resin.

5. The method for preparing aluminum capacitor anode foil based on microwave sintering according to claim 1, characterized in that: The conductivity of the deionized water in step 5 is σ≤5×10 -4 S / m.

6. The method for preparing aluminum capacitor anode foil based on microwave sintering according to claim 1, characterized in that: The concentration of the diammonium phosphate solution in step six is ​​0.3 mol / L.

7. The method for preparing aluminum capacitor anode foil based on microwave sintering according to claim 1, characterized in that: The formation voltage used in the formation treatment in step 7 is 530V and the current density is 1.5A / cm 2 ~3A / cm 2 , the chemical forming liquid is a boric acid solution system.

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