Electrode foil processing method for high-durability solid-state capacitor

Abstract

The invention provides a treatment method of an electrode foil for a high-durability solid capacitor. A mixed solution of 0.8-1.2 wt% of HF and 0.8-1.5 ppm of iron ions is added in phosphoric acid pretreatment. The aluminum foil is placed in a phosphoric acid mixed solution at the temperature of 45-75 DEG C, and oil stains, impurities and dirty spots on the surface of the aluminum foil are removed after a reaction for a period of time. A trace amount of iron ions are added to play a role in passivation, but a trace amount of HF is added to generate a strong dissolution effect on a passivation film. Through the test, the heteroplasmon on the surface of the aluminum foil is cleared, the surface state of the sample is activated, the generation of a conversion film is promoted, the distribution of etched holes is more uniform, the later expanded holes are more tightly distributed, and thus the effect of improving the durability is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum foil production for aluminum electrolytic capacitors, and particularly relates to the electrolytic corrosion technology of electrode foils for solid capacitors. Background Art

[0002] For the anode foil of aluminum electrolytic capacitors, in order to obtain a higher specific capacitance, a mixed solution of sulfuric acid and hydrochloric acid is usually used for pretreatment. However, the formed oxide film has poor durability and toughness, and cannot meet the long-term use requirements. Summary of the Invention

[0003] Object of the Invention / Technical Problem: Aiming at the problems existing in the prior art, the present invention provides a method for treating electrode foils for solid capacitors with high durability. On the basis of improving and maintaining the good specific capacitance of the aluminum foil, the durability and toughness of the etched foil are improved, which can cope with more demanding usage environments, reduce the replacement of materials, and is more environmentally friendly to a certain extent.

[0004] Summary of the Invention: To achieve the above technical object, the present invention is realized through the following technical solutions: A method for treating electrode foils for solid capacitors with high durability, comprising the following steps: (1) Pretreatment The aluminum foil is immersed in the pretreatment solution for etching for 1 - 3 minutes and then washed with distilled water; the pretreatment solution is a mixed solution of 1 - 3 wt% phosphoric acid, 0.8 - 1.2 wt% hydrofluoric acid and 1 - 3 ppm iron ions, and the pretreatment temperature is 70 ± 5 °C; (2) Pre - etching The aluminum foil after pretreatment is subjected to alternating current electrolytic etching in a mixed solution of 0.8 - 1.2 wt% sulfuric acid and 0.8 - 1.2 wt% hydrochloric acid; (3) Intermediate treatment After the aluminum foil undergoes initial etching and is washed with distilled water, it is immersed in a mixed solution of 7 - 18 wt% hydrochloric acid + 0.8 - 1.2 wt% sulfuric acid and 0.1 - 7 ppm copper ions for intermediate treatment, and then washed with distilled water; (4) Pore - expanding etching The aluminum foil continues to be subjected to alternating current electrolytic etching in 1 - 10 wt% hydrochloric acid or 3 - 10 wt% nitric acid solution; (5) Post - treatment The aluminum foil is immersed in 3 - 15 wt% nitric acid at 40 - 55 °C for 2 - 5 minutes, then rinsed with distilled water, and dried at 200 - 350 °C to complete.

[0005] Furthermore, the pre - etching temperature is 50 - 70 °C, the current density is 20 - 80 A / dm², and the charge is 600 - 3000 C / dm².

[0006] Further, the medium treatment temperature is 80 - 90°C, and the soaking time is 0.5 - 2 min.

[0007] Further, during the reaming corrosion, the temperature is 25 - 50°C, the current density is 10 - 50 A / dm², and the electric quantity is 4500 - 8000 C / dm².

[0008] Beneficial effects: According to the above technical solution, compared with the prior art, the impurity enrichment area on the aluminum foil surface is strictly controlled, excessive impurity accumulation is greatly reduced, and the aluminum foil surface can be kept clean and tidy with uniform arrangement and distribution. As a result, the later reaming holes are more closely distributed and there will be no local tearing or collapse, thereby improving the durability of the aluminum foil. Specific embodiments

[0009] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. Unless otherwise specifically stated, the relative arrangements, expressions, and numerical values of the components and steps described in these embodiments do not limit the scope of the present invention. Technologies, methods, and devices known to those of ordinary skill in the relevant fields may not be discussed in detail, but should be regarded as part of the authorization specification when appropriate. In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values.

[0010] The main purpose of the pre - treatment of the present invention is to remove the oil stains, impurities, and natural oxide film on the aluminum foil surface, so that the arrangement and distribution of the aluminum foil surface are uniform, which is beneficial to the formation of excellent initial corrosion holes during pre - corrosion. Almost all the initial corrosion areas are impurity enrichment areas. Therefore, the cleaning and content distribution treatment of impurities are very important, which will affect the service tolerance of the finished foil. By adding trace iron ions and HF to the pre - treatment mixed solution of hydrochloric acid and sulfuric acid, after several experiments, it is found that the durability of the final product is significantly better than that of the prior art. The technological process of the present invention is as follows: pre - treatment - pre - corrosion - medium treatment - corrosion - post - treatment - drying. The following details the specific process: Using soft - state aluminum foil with a thickness of 104 μm Pre - treatment: Place the aluminum foil in a phosphoric acid pre - treatment solution at 70°C (adding a mixed solution of 0.8 - 1.2 wt% HF + 0.8 - 1.5 ppm iron ions), and soak for 1 - 3 minutes; Rinse with clear water; Pre-corrosion: Control the temperature in the tank at 50 - 70 °C, the current density at 20 - 100 A / dm², and the electric quantity at 600 - 3000 C / dm²; Rinse with clear water; Medium treatment: Control the temperature at 80 - 90 °C and soak in a phosphoric acid aqueous solution with a concentration of 0.2 - 0.8 wt% for 0.5 - 2 minutes; Rinse with clear water; AC corrosion: Control the temperature in the tank at 25 - 50 °C, the current density at 10 - 50 A / dm², and the electric quantity at 4500 - 8000 C / dm²; Rinse with clear water; Post-treatment: Control the temperature at 40 - 55 °C and soak in a nitric acid aqueous solution with a concentration of 5 - 16 wt% for 2 - 5 minutes; Rinse with clear water; Drying: Dry the foil in an oven at 200 - 350 °C.

[0011] Example 1: Place the aluminum foil in the pretreatment without any additive solution and with a phosphoric acid concentration of 2 wt% for 80 seconds.

[0012] Example 2: React the aluminum foil in a mixed solution with a phosphoric acid concentration of 2 wt%, an HF concentration of 0.9 wt%, and an additional 0.8 ppm of iron ions.

[0013] Example 3: React the aluminum foil in a mixed solution with a phosphoric acid concentration of 2 wt%, an HF concentration of 0.8 wt%, and an additional 0.9 ppm of iron ions.

[0014] Example 4: React the aluminum foil in a mixed solution with a phosphoric acid concentration of 2 wt%, an HF concentration of 1.0 wt%, and an additional 1.0 ppm of iron ions.

[0015] Example 5: React the aluminum foil in a mixed solution with a phosphoric acid concentration of 2 wt%, an HF concentration of 1.1 wt%, and an additional 1.2 ppm of iron ions.

[0016] Example 6: React the aluminum foil in a mixed solution with a phosphoric acid concentration of 2 wt%, an HF concentration of 1.2 wt%, and an additional 1.5 ppm of iron ions.

[0017] Table 1 shows the performance of the etched foils after the treatment of each example

[0018] It can be seen from the experimental results that by adding 0.8 - 1.2 wt% HF + 0.8 - 1.5 ppm of iron ions to the pretreatment mixed solution, the durability and bending resistance of the etched foil have been significantly improved.

[0019] The above are only some embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for treating an electrode foil for a highly durable solid capacitor, characterized in that It includes the following steps: (1) Pretreatment The aluminum foil is immersed in the pretreatment solution for 1 - 3 minutes for corrosion and then washed with distilled water; the pretreatment solution is a mixed solution of 1 - 3 wt% phosphoric acid, 0.8 - 1.2 wt% hydrofluoric acid and 1 - 3 ppm iron ions, and the pretreatment temperature is 70 ± 5°C; (2) Pre - corrosion The aluminum foil after pretreatment is subjected to alternating current electrolytic corrosion in a mixed solution of 0.8 - 1.2 wt% sulfuric acid and 0.8 - 1.2 wt% hydrochloric acid; (3) Intermediate treatment After the aluminum foil undergoes initial corrosion and is washed with distilled water, it is immersed in a mixed solution of 7 - 18 wt% hydrochloric acid + 0.8 - 1.2 wt% sulfuric acid and 0.1 - 7 ppm copper ions for intermediate treatment and then washed with distilled water; (4) Hole - expanding corrosion The aluminum foil continues to be subjected to alternating current electrolytic corrosion in 1 - 10 wt% hydrochloric acid or 3 - 10 wt% nitric acid solution; (5) Post - treatment The aluminum foil is immersed in 3 - 15 wt% nitric acid at 40 - 55°C for 2 - 5 minutes, then rinsed with distilled water and dried at 200 - 350°C to complete.

2. The method for treating an electrode foil for a highly durable solid-state capacitor according to claim 1, characterized in that: The pre - corrosion temperature is 50 - 70°C, the current density is 20 - 80 A / dm², and the electric quantity is 600 - 3000 C / dm².

3. The method for treating an electrode foil for a highly durable solid capacitor according to claim 1, characterized in that: The intermediate treatment temperature is 80 - 90°C, and the immersion time is 0.5 - 2 minutes.

4. The method for treating the electrode foil for a highly durable solid capacitor according to claim 1, wherein: The temperature during hole - expanding corrosion is 25 - 50°C, the current density is 10 - 50 A / dm², and the electric quantity is 4500 - 8000 C / dm².

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