A pretreatment method for improving the specific capacitance of low-voltage forming foil and its application

Abstract

The present invention discloses a pretreatment method for preparing high specific capacitance low-voltage formation foil and its application. The pretreatment method is carried out by soaking aluminum foil in a pretreatment solution, and the pretreatment solution contains components with the following concentrations: 0.01 - 0.5 g / L triethanolamine, 0.01 - 0.5 g / L organic weak acid; the soaking time is not less than 10 s. The pretreatment method forms a trace amount of aluminum amide on the surface of the aluminum foil, which can increase the dielectric constant of alumina and enable the specific capacitance of the pretreated aluminum foil to increase after corrosion and formation; the organic weak acid plays a neutralizing role to avoid the problem of pore blockage caused by the generation of aluminum hydroxide and the reduction of specific capacitance. The low-voltage formation foil prepared by adopting this process has a relatively high specific capacitance and good performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of etched foils, and particularly relates to a pretreatment method for improving the specific capacitance of low-voltage etched foils and its application. Background Art

[0002] As a basic electronic component, an aluminum electrolytic capacitor can play the role of passing alternating current and blocking direct current, and realizing functions such as filtering, rapid charging and discharging. With the development of miniaturization of electronic devices as a whole, there is an urgent need to reduce the volume and increase the specific capacitance of low-voltage aluminum electrolytic capacitors. As the core material in low-voltage aluminum electrolytic capacitors, low-voltage etched foils play a decisive role in various characteristics of the capacitors.

[0003] Generally, an aluminum electrolytic capacitor is a capacitive element formed by winding an anode foil, an electrode paper, a cathode foil, and an electrolytic paper alternately and impregnating with an electrolyte solution. The existing chemical conversion method for low-voltage etched foils generally includes the following steps: taking an etched aluminum foil, placing it in an aqueous solution of ammonium adipate and adipate salts, performing chemical conversion and water washing, performing passivation treatment in a phosphoric acid solution with a concentration of 1-8%, and then water washing; then placing it in an aqueous solution of dihydrogen phosphate, performing chemical conversion and water washing to obtain. However, the specific capacitance of the low-voltage etched foils obtained by the conventional chemical conversion method is relatively low, generally not exceeding 90 μF / cm 2 , and in many cases, it is impossible to meet the requirements of customers.

[0004] Therefore, it is necessary to develop a pretreatment method for improving the specific capacitance of low-voltage etched foils, so that the specific capacitance of the prepared low-voltage etched foils can meet the requirements of customers, reduce the size of the capacitors, and meet the requirements of miniaturization. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a pretreatment method for improving the specific capacitance of low-voltage etched foils. By pretreating with an acidic aqueous solution of triethanolamine and then performing etching and chemical conversion, the specific capacitance of the low-voltage etched foils can be improved.

[0006] To achieve the above purpose, the present invention is realized through the following technical solutions:

[0007] A pretreatment method for improving the specific capacitance of low-voltage etched foils includes the following steps:

[0008] Pretreatment: Immerse the aluminum foil in a pretreatment solution. The pretreatment solution contains the following components in concentrations: 0.01-0.5 g / L of triethanolamine, 0.01-0.5 g / L of an organic weak acid; the immersion time is not less than 10 s.

[0009] The inventor found that when pretreating aluminum foil with an aqueous solution of triethanolamine and organic weak acid at a specific concentration, triethanolamine can react with the aluminum foil to form a trace amount of aluminum amide, which can increase the dielectric constant of alumina and the specific capacitance of the aluminum foil after etching and chemical conversion; the organic weak acid plays a neutralizing role, otherwise aluminum hydroxide will be generated, causing pore blockage and reducing the specific capacitance.

[0010] Preferably, the pretreatment solution contains the following components in the following concentrations: 0.05 - 0.5 g / L of triethanolamine and 0.05 - 0.5 g / L of organic weak acid.

[0011] More preferably, the concentrations of triethanolamine and organic weak acid in the pretreatment solution are the same. By further adjusting the concentrations of triethanolamine and organic weak acid in the pretreatment solution, when their concentrations are the same, the specific capacitance of the low-voltage chemical conversion foil can be further increased.

[0012] More preferably, the pretreatment solution contains the following components in the following concentrations: 0.05 - 0.5 g / L of triethanolamine and 0.05 - 0.5 g / L of organic weak acid; the concentrations of triethanolamine and organic weak acid are the same.

[0013] Preferably, the organic weak acid is one or more of citric acid, tartaric acid or lactic acid.

[0014] Preferably, the soaking time is 10 s - 180 s.

[0015] Another object of the present invention is to provide a high-specific-capacitance pretreated aluminum foil.

[0016] Another object of the present invention is to provide a high-specific-capacitance low-voltage chemical conversion foil.

[0017] Another object of the present invention is to provide a preparation method of a high-specific-capacitance low-voltage chemical conversion foil.

[0018] A preparation method of a high-specific-capacitance low-voltage chemical conversion foil includes the following steps: subjecting the high-specific-capacitance pretreated aluminum foil obtained by the above method to first-stage chemical conversion, cleaning, passivation treatment, heat treatment, second-stage chemical conversion, cleaning, and drying in sequence.

[0019] Specifically, the preparation method of the high-specific-capacitance low-voltage chemical conversion foil includes the following steps:

[0020] S1. Using the high-specific-capacitance pretreated aluminum foil obtained by the pretreatment method;

[0021] S2. Placing the high-specific-capacitance pretreated aluminum foil into a first electrolyte solution for first-stage chemical conversion and first water washing;

[0022] S3. Subjecting the aluminum foil after the first water washing in S2 to phosphoric acid passivation treatment, then heat treatment, and second water washing;

[0023] S4. Place the aluminum foil after the second water wash in step S3 into the second electrolyte for secondary formation cleaning and drying.

[0024] In the above solution, there is trace aluminum amide on the surface of the high specific capacitance pre-treated aluminum foil after pretreatment. After phosphoric acid passivation treatment and then heat treatment, the water hydration resistance of the aluminum foil can be effectively improved, and the specific capacitance of the aluminum foil can be further increased.

[0025] In the present invention, the first electrolyte commonly used in the existing low-voltage formed foil preparation method can be referred to. Preferably, in step S2, the first electrolyte is an aqueous solution of adipic acid salt with a concentration of 3-15 wt.%.

[0026] Specifically, the adipic acid salt is one or several of ammonium adipate, sodium adipate or potassium adipate.

[0027] Preferably, in step S2, the formation temperature of the first stage of formation is 65-95 °C, the current density is 20-25 mA / cm 2 , and the formation time is 18-22 min.

[0028] In the present invention, the phosphoric acid passivation treatment can be referred to the existing low-voltage formed foil preparation method. Preferably, in step S2, the phosphoric acid passivation treatment is to place the aluminum foil after the first water wash in an aqueous solution of phosphoric acid with a concentration of 1-8 wt.%; the temperature of the phosphoric acid passivation treatment is 50-80 °C.

[0029] Preferably, in step S3, the temperature of the heat treatment is 300-550 °C, and the time is 1-5 min.

[0030] Preferably, in step S3, the heat treatment is carried out in a drying furnace under an air atmosphere.

[0031] Preferably, in step S4, the second electrolyte is an aqueous solution of ammonium dihydrogen phosphate with a concentration of 0.1-2 wt.%.

[0032] Preferably, in step S4, the formation temperature of the secondary formation is 50-95 °C, the current density is 20-25 mA / cm 2 , and the formation time is 4-6 min.

[0033] The present invention also protects the high specific capacitance low-voltage formed foil prepared by the above method.

[0034] The specific capacitance of the high specific capacitance low-voltage formed foil ≥ 95 μF / cm 2 .

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention provides a pretreatment method for preparing high specific capacitance low-voltage forming foil and its application. The pretreatment method uses a mixed solution of triethanolamine and organic weak acid to treat the aluminum foil, generating trace amounts of aluminum amide on the surface of the aluminum foil, which can increase the dielectric constant of alumina and increase the specific capacitance of the aluminum foil after corrosion and forming; then, after forming in an aqueous solution of adipic acid and washing with water, passivating in a phosphoric acid solution, and then subjecting to heat treatment and ammonium dihydrogen phosphate forming, the water hydration resistance of the aluminum foil can be effectively improved, further increasing the specific capacitance of the aluminum foil, and the prepared low-voltage forming foil has a relatively high specific capacitance. Detailed implementation manners

[0037] The following further elaborates on the present invention in conjunction with specific embodiments. The embodiments are only used to explain the present invention and are not intended to limit the scope of the present invention. The test methods used in the following embodiments are all conventional methods unless otherwise specified; the materials, reagents, etc. used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0038] The aluminum foil used in the examples and comparative examples is of the ls90 specification, with an aluminum foil purity of ≥99.98%, purchased from Dongyangguang Precision Foil Co., Ltd.; the triethanolamine, citric acid, adipic acid, phosphoric acid, and ammonium dihydrogen phosphate used are all commercially available analytical pure.

[0039] Example 1

[0040] A pretreatment method for increasing the specific capacitance of low-voltage forming foil includes the following steps:

[0041] Immerse the aluminum foil in the pretreatment solution for 3 minutes to obtain high specific capacitance pretreated aluminum foil. The pretreatment solution contains the following components in concentrations: 0.25 g / L triethanolamine and 0.25 g / L citric acid.

[0042] Example 2

[0043] A pretreatment method for increasing the specific capacitance of low-voltage forming foil includes the following steps:

[0044] Immerse the aluminum foil in the pretreatment solution for 3 minutes to obtain high specific capacitance pretreated aluminum foil. The pretreatment solution contains the following components in concentrations: 0.01 g / L triethanolamine and 0.01 g / L citric acid.

[0045] Example 3

[0046] A pretreatment method for increasing the specific capacitance of low-voltage forming foil includes the following steps:

[0047] Immerse the aluminum foil in the pretreatment solution for 3 minutes to obtain high specific capacitance pretreated aluminum foil. The pretreatment solution contains the following components in concentrations: 0.05 g / L triethanolamine and 0.05 g / L citric acid.

[0048] Example 4

[0049] A pretreatment method for improving the specific capacitance of low-voltage formed foil, comprising the following steps:

[0050] Soak the aluminum foil in the pretreatment solution for 3 min to obtain a high-specific-capacitance pretreated aluminum foil, and the pretreatment solution contains components with the following concentrations: 0.2 g / L triethanolamine, 0.2 g / L citric acid.

[0051] Example 5

[0052] A pretreatment method for improving the specific capacitance of low-voltage formed foil, comprising the following steps:

[0053] Soak the aluminum foil in the pretreatment solution for 3 min to obtain a high-specific-capacitance pretreated aluminum foil, and the pretreatment solution contains components with the following concentrations: 0.5 g / L triethanolamine, 0.5 g / L citric acid.

[0054] Example 6

[0055] A pretreatment method for improving the specific capacitance of low-voltage formed foil, comprising the following steps:

[0056] Soak the aluminum foil in the pretreatment solution for 10 s to obtain a high-specific-capacitance pretreated aluminum foil, and the pretreatment solution contains components with the following concentrations: 0.2 g / L triethanolamine, 0.2 g / L citric acid.

[0057] Example 7

[0058] A pretreatment method for improving the specific capacitance of low-voltage formed foil, comprising the following steps:

[0059] Pretreatment: Soak the aluminum foil in the pretreatment solution for 3 min to obtain a high-specific-capacitance pretreated aluminum foil, and the pretreatment solution contains components with the following concentrations: 0.2 g / L triethanolamine, 0.48 g / L citric acid.

[0060] Example 8

[0061] A pretreatment method for improving the specific capacitance of low-voltage formed foil, comprising the following steps:

[0062] Pretreatment: Soak the aluminum foil in the pretreatment solution for 3 min to obtain a high-specific-capacitance pretreated aluminum foil, and the pretreatment solution contains components with the following concentrations: 0.48 g / L triethanolamine, 0.2 g / L citric acid.

[0063] Comparative Example 1

[0064] A pretreatment method for improving the specific capacitance of low-voltage formed foil, comprising the following steps:

[0065] Pretreatment: Soak the aluminum foil in the pretreatment solution for 3 min to obtain a pretreated aluminum foil, and the pretreatment solution contains components with the following concentrations: 0.2 g / L triethanolamine.

[0066] Comparative Example 2

[0067] A pretreatment method for improving the specific capacitance of low-voltage formed foil, comprising the following steps:

[0068] Pretreatment: Immerse the aluminum foil in the pretreatment solution for 3 min to obtain a high-specific-capacitance pretreated aluminum foil. The pretreatment solution contains the following components in concentration: 0.2 g / L citric acid.

[0069] Example 9

[0070] A preparation method of high-specific-capacitance low-voltage formed foil comprises the following steps:

[0071] First-stage forming treatment: Place the high-specific-capacitance pretreated aluminum foil prepared in the above Examples 1-8 in an aqueous solution of 15 wt.% adipic acid, carry out first-stage forming and first washing; the forming temperature of the first-stage forming is 75 °C, and the current density is 20 mA / cm 2 , and the forming time is 18 min;

[0072] Phosphoric acid passivation treatment: Place the aluminum foil after the first washing in an aqueous solution of 1 wt.% phosphoric acid for phosphoric acid passivation treatment, and the temperature is 50 °C;

[0073] Heat treatment: Place the aluminum foil after phosphoric acid passivation treatment in a drying furnace and carry out heat treatment in an air atmosphere. The heat treatment temperature is 300 °C and the time is 3 min;

[0074] Second-stage forming treatment: Place the aluminum foil after heat treatment in an aqueous solution of 2 wt.% ammonium dihydrogen phosphate for second-stage forming; the forming temperature of the second-stage forming is 75 °C, and the current density is 20 mA / cm 2 , and the forming time is 4 min, then wash and dry to obtain high-specific-capacitance low-voltage formed foils 1-8.

[0075] Example 10 (heat treatment temperature is 450 °C)

[0076] A preparation method of high-specific-capacitance low-voltage formed foil comprises the following steps:

[0077] First-stage forming treatment: Place the high-specific-capacitance pretreated aluminum foil prepared in Example 1 above in an aqueous solution of 15 wt.% adipic acid, carry out first-stage forming and first washing; the forming temperature of the first-stage forming is 75 °C, and the current density is 20 mA / cm 2 , and the forming time is 18 min;

[0078] Phosphoric acid passivation treatment: Place the aluminum foil after the first washing in an aqueous solution of 1 wt.% phosphoric acid for phosphoric acid passivation treatment, and the temperature is 50 °C;

[0079] Heat treatment: Place the aluminum foil after phosphoric acid passivation treatment in a drying furnace and conduct heat treatment in an air atmosphere. The heat treatment temperature is 450 °C and the time is 3 min;

[0080] Second-stage formation treatment: Place the aluminum foil after heat treatment in an aqueous solution of 2 wt.% ammonium dihydrogen phosphate for second-stage formation; the formation temperature for the second-stage formation is 75 °C and the current density is 20 mA / cm 2 , the formation time is 4 min, and then wash with water and dry to obtain high specific capacitance low-voltage formed foil 9.

[0081] Example 11 (heat treatment temperature is 520 °C)

[0082] A preparation method of high specific capacitance low-voltage formed foil includes the following steps:

[0083] First-stage formation treatment: Place the high specific capacitance pre-treated aluminum foil prepared in Example 1 above in an aqueous solution of 15 wt.% adipic acid ammonium for first-stage formation and first water washing; the formation temperature for the first-stage formation is 75 °C and the current density is 20 mA / cm 2 , the formation time is 18 min;

[0084] Phosphoric acid passivation treatment: Place the aluminum foil after the first water washing in a 1 wt.% phosphoric acid aqueous solution for phosphoric acid passivation treatment at a temperature of 50 °C;

[0085] Heat treatment: Place the aluminum foil after phosphoric acid passivation treatment in a drying furnace and conduct heat treatment in an air atmosphere. The heat treatment temperature is 520 °C and the time is 3 min;

[0086] Second-stage formation treatment: Place the aluminum foil after heat treatment in an aqueous solution of 2 wt.% ammonium dihydrogen phosphate for second-stage formation; the formation temperature for the second-stage formation is 75 °C and the current density is 20 mA / cm 2 , the formation time is 4 min, and then wash with water and dry to obtain high specific capacitance low-voltage formed foil 10.

[0087] Example 12 (heat treatment temperature is 550 °C)

[0088] A preparation method of high specific capacitance low-voltage formed foil includes the following steps:

[0089] First-stage formation treatment: Place the high specific capacitance pre-treated aluminum foil prepared in Example 1 above in an aqueous solution of 15 wt.% adipic acid ammonium for first-stage formation and first water washing; the formation temperature for the first-stage formation is 75 °C and the current density is 20 mA / cm 2 , the formation time is 18 min;

[0090] Phosphoric acid passivation treatment: The aluminum foil after the first-stage water washing is placed in a 1 wt.% phosphoric acid aqueous solution for phosphoric acid passivation treatment at a temperature of 50 °C;

[0091] Heat treatment: The aluminum foil after phosphoric acid passivation treatment is placed in a drying furnace for heat treatment in an air atmosphere. The heat treatment temperature is 550 °C and the time is 3 min;

[0092] Second-stage formation treatment: The aluminum foil after heat treatment is placed in a 2 wt.% ammonium dihydrogen phosphate aqueous solution for second-stage formation; the formation temperature of the second-stage formation is 75 °C and the current density is 20 mA / cm 2 , the formation time is 4 min, and then it is washed with water and dried to obtain the high specific capacitance low-voltage formed foil 11.

[0093] Comparative example 3

[0094] A method for preparing a low-voltage formed foil includes the following steps:

[0095] First-stage formation treatment: The high specific capacitance pre-treated aluminum foil prepared in the above comparative examples 1-2 is placed in a 15 wt.% adipic acid aqueous solution for first-stage formation and first-stage water washing; the formation temperature of the first-stage formation is 75 °C and the current density is 20 mA / cm 2 , the formation time is 18 min;

[0096] Phosphoric acid passivation treatment: The aluminum foil after the first-stage water washing is placed in a 1 wt.% phosphoric acid aqueous solution for phosphoric acid passivation treatment at a temperature of 50 °C;

[0097] Heat treatment: The aluminum foil after phosphoric acid passivation treatment is placed in a drying furnace for heat treatment in an air atmosphere. The heat treatment temperature is 300 °C and the time is 3 min;

[0098] Second-stage formation treatment: The aluminum foil after heat treatment is placed in a 2 wt.% ammonium dihydrogen phosphate aqueous solution for second-stage formation; the formation temperature of the second-stage formation is 75 °C and the current density is 20 mA / cm 2 , the formation time is 4 min, and then it is washed with water and dried to obtain the comparative low-voltage formed foils 1-2.

[0099] Performance test

[0100] The high specific capacitance low-voltage formed foils 1-8 and the comparative low-voltage formed foils 1-3 prepared by the above method are subjected to performance tests. The specific test method is as follows: According to the EIAJ RC-2364A standard method, a specific capacitance tester is used to measure the specific capacitance and voltage. The measurement results are shown in Table 1.

[0101] Table 1 Test results of high specific capacitance low-voltage formed foils 1-8 and comparative low-voltage formed foils 1-3

[0102] <![CDATA[Specific capacitance (μF / cm 2 )]]> Voltage (V) High specific capacitance low voltage etched foil 1 95.88 21.0 High specific capacitance low voltage etched foil 2 95.78 21.0 High specific capacitance low voltage etched foil 3 97.45 21.2 High specific capacitance low voltage etched foil 4 96.54 21.7 High specific capacitance low voltage etched foil 5 97.31 21.5 High specific capacitance low voltage etched foil 6 95.32 21.3 High specific capacitance low voltage etched foil 7 90.04 21.2 High specific capacitance low voltage etched foil 8 91.04 21.3 High specific capacitance low voltage etched foil 9 95.30 21.2 High specific capacitance low voltage etched foil 10 95.10 21.7 High specific capacitance low voltage etched foil 11 95.01 21.9 Comparative low voltage etched foil 1 80.45 21.5 Comparative low voltage etched foil 2 75.54 21.2

[0103] As can be seen from Table 1, the specific capacitance of the high specific capacitance low-voltage forming foil prepared by using the pretreatment method of the present invention is ≥90 μF / cm 2 ; by further adjusting the concentration of the pretreatment liquid in the pretreatment process, when the concentrations of triethanolamine and citric acid in the pretreatment liquid are the same, the specific capacitance of the prepared high specific capacitance low-voltage forming foil can be further increased, and the specific capacitance can reach 95 μF / cm 2 or more.

[0104] By comparing high specific capacitance low-voltage forming foils 1-5 and comparative low-voltage forming foils 1-2, it can be seen that when the pretreatment liquid in the pretreatment process only contains triethanolamine, the specific capacitance of the prepared comparative low-voltage forming foil is only 80.45 μF / cm 2 , which is because when there is no organic acid in the pretreatment liquid, aluminum hydroxide is generated in the aluminum foil, causing pore blockage and resulting in a decrease in the specific capacitance of the prepared low-voltage forming foil; when the pretreatment liquid only contains citric acid, the specific capacitance of the prepared low-voltage forming foil is also relatively low, only reaching 75.54 μF / cm 2 .

[0105] Obviously, the above-mentioned embodiments of the present invention are merely examples for clearly illustrating the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made on the basis of the above description. Any other changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A pretreatment method for improving the specific capacitance of low-voltage formed foil, comprising the following steps: Soak the aluminum foil in a pretreatment solution, the pretreatment solution containing components in the following concentrations: 0.01 - 0.5 g / L triethanolamine, 0.01 - 0.5 g / L organic weak acid; the soaking time is not less than 10 s; the concentrations of triethanolamine and organic weak acid in the pretreatment solution are the same; the organic weak acid is one or more of citric acid, tartaric acid or lactic acid.

2. The pretreatment method according to claim 1, wherein The pretreatment solution contains components in the following concentrations: 0.05 - 0.5 g / L triethanolamine, 0.05 - 0.5 g / L organic weak acid.

3. The pretreatment method according to claim 1, wherein The soaking time is 10 s - 180 s.

4. A high specific capacitance pre-treated aluminum foil, characterized in that, Prepared by using the pretreatment method according to any one of claims 1 - 3.

5. A preparation method of a high specific capacitance low-voltage formation foil, characterized in that, The high-specific-capacitance pretreated aluminum foil obtained in claim 4 is successively subjected to first-stage forming, cleaning, passivation treatment, heat treatment, second-stage forming, cleaning, and drying.

6. A preparation method of a high specific capacitance low-voltage formation foil, characterized in that, Comprising the following steps: S1. The high-specific-capacitance pretreated aluminum foil obtained by using the pretreatment method according to any one of claims 1 - 3; S2. Put the high-specific-capacitance pretreated aluminum foil into a first electrolyte solution for first-stage forming and first water washing; S3. Subject the aluminum foil after the first water washing in S2 to phosphoric acid passivation treatment, then to heat treatment and second water washing; S4. Put the aluminum foil after the second water washing in S3 into a second electrolyte solution for second-stage forming cleaning and drying.

7. The preparation method according to claim 6, characterized in that, The temperature of the heat treatment is 300 - 550 °C.

8. A high specific capacitance low voltage forming foil, characterized in that, Prepared by using the preparation method according to any one of claims 5 - 7.