JPS636639B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing aluminum alloy foil for electrolytic capacitor electrodes. Aluminum electrode foils for electrolytic capacitors are generally subjected to electrical or chemical etching treatment in order to expand their effective surface area and increase capacitance per unit volume. In order to increase this area expansion ratio, various studies have been made to increase the number of etching holes as much as possible. However,
Conventional electrolytic etching techniques generally have the problem that when attempting to increase the number of etching holes, the surface of the foil also dissolves at the same time, resulting in increased corrosion loss and loss of mechanical strength. For this reason, the area enlargement ratio is limited by the mechanical strength after etching, and it has been difficult to significantly increase the area enlargement ratio. The present invention solves these problems and provides a method for manufacturing an aluminum alloy foil for capacitor electrodes, which increases the area expansion ratio and significantly improves the capacitance, without sacrificing mechanical strength. This is what I am trying to do. Therefore, this invention has aluminum purity of 99.9%.
Using an aluminum alloy foil containing 0.5 to 100 wt-ppm of at least one of phosphorus and arsenic, the aluminum alloy foil is treated with 2 to 15% of chlorine ions and porous oxidized by anode polarization. 50 containing 1-35% acid to form a film
Current density 5-40A/dm ² in aqueous solution at ~100℃
After a preliminary etching treatment using a direct current of
In an aqueous solution at 50-100℃ containing 3%
It is characterized by a post-etching process using a direct current of 0.5 to 7 A/dm ² . This will be explained in more detail below. [Aluminum Alloy Foil Composition] Phosphorus and arsenic contained in the aluminum alloy foil used in this invention are equivalent in that they increase the capacitance of the foil, and one or both of these are added to aluminum. However, if the total content of both elements or the content of either element in the foil is less than 0.5wt-ppm (0.00005wt%), the effect of increasing capacitance is small, and 100wt-ppm
(0.03wt%), corrosion loss will be large and this is not preferable in terms of maintaining the strength of the foil. Therefore, this content should be selected within the range of 0.5 to 100 wt-ppm, with a range of 1.0 to 30 ppm being particularly preferred. The reason why the inclusion of phosphorus and/or arsenic increases the capacitance of the foil is considered to be as follows. That is, the difference in electrical potential between aluminum and phosphorus and arsenic with respect to the etching solution acts as a driving force for etching, significantly increasing the number of etching holes, and phosphorus and arsenic are removed in the material by heating. Since it is easy to diffuse, it is evenly dispersed on the material surface due to the thermal history during the manufacturing process of the foil, and at that time, it is also dispersed along with other contained elements, so it is assumed that this is because the etching holes are evenly distributed. . However, if their content exceeds 100wt-ppm, the density of etching holes increases, but the surface of the foil also dissolves, resulting in a decrease in capacitance and strength. It will be done. On the other hand, it is well known that aluminum foil for capacitor electrodes requires a purity of 99.9% or higher;
99.99% or higher is preferable. Therefore, it is naturally permissible for the aluminum alloy foil used in the present invention to contain other elements as inevitable impurities in addition to phosphorus and/or arsenic. In addition, conventionally, this type of aluminum alloy foil for capacitor electrodes has been actively added with other trace elements in order to increase the number of etched holes per unit area. In addition to the inclusion of , phosphorus, and arsenic, cases where such forcibly added elements are additionally included are also included in the scope. Such elements include, for example, copper, strontium, vanadium, titanium, manganese, magnesium, zinc, indium, tin,
Examples include lead, bismuth, boron, silver, gallium, cadmium, zirconium, thorium, iron, silicon, etc., and the content is generally 0.1 to 5000wt−
Within ppm range. When these elements are contained in addition to phosphorus and arsenic, in addition to the mere summation of the effects of phosphorus and arsenic with other elements, a more synergistic effect is expected. Although it is expected that there will be cases where
In any case, the present invention is included within the scope of the invention as long as the effects of containing phosphorus and/or arsenic are achieved. [First-stage etching process] If the chlorine ion concentration in the etching solution in the first-stage etching process is less than 2%, the desired etching effect cannot be obtained, and if it exceeds 15%, the aluminum foil surface will completely dissolve. progresses.
Therefore, within the above range, particularly preferably 5 to 8%
It is better to set it as a degree. The acid to be added to the aqueous solution containing chloride ions should be selected from those capable of forming an oxide film as porous as possible; for example, sulfuric acid, oxalic acid, phosphoric acid, chromic acid, etc. can be preferably used. Among these, sulfuric acid is particularly preferred since it can form a large number of etching holes per unit area. The amount of the above acid added varies depending on the type of acid, but if it is less than 1%, the formation of a porous oxide film that will become the etching nucleus will not be sufficient, whereas if it exceeds 35%, the entire surface will not dissolve. happen. Therefore, it should be within the range of 1 to 35%,
Particularly preferably, the range is 10 to 20%. The reason why good results can be obtained by adding the acid in this range is that by anodically polarizing the aluminum foil in a solution containing the acid, the foil surface has more than 100 million pores per ¹ mm2. A so-called porous oxide film is formed, the pores of which are eroded by chlorine ions, and the areas other than the pores are covered with the oxide film, which suppresses surface dissolution, and as a result, compared to etching using only chlorine ions, This is thought to be because the number of etching holes becomes very large and deep. The temperature of the etching solution used in the pre-etching process also has an important effect on the effectiveness. If the temperature is less than 50°C, the etching effect will be small, and if it exceeds 100°C, the entire surface will dissolve. Therefore, it is preferable to carry out the treatment at a temperature in the range of 50 to 100°C, particularly preferably in the range of 70 to 90°C. On the other hand, if the current density is less than 5A/ ^dm2 , the etching effect is still poor;
When it exceeds 40 A/dm ² , total melting occurs. Within this range, it should therefore particularly preferably be between 10 and 25 A/dm ² . In addition, the amount of electricity for the first stage etching is 500 to 3000
The coulomb/ ^dm2 range is good, especially from 1500 to
A range of 2000 coulombs/dm ² is optimal. That is,
If it is less than 500 coulombs/dm ² , the etching effect will be small, and if it exceeds 3000 coulombs/dm ² , the entire surface will be dissolved. The pre-etching step is carried out under the conditions of addition of a relatively high concentration of oxidizing acid to the etching solution, high solution temperature, and high current density, as described above. Therefore, such etching is very harsh, and as the etching progresses, the electrical resistance inside the etching hole increases due to generated gas, dissolved aluminum ions, etc., and the etching within the etching hole stops. As a result, surface dissolution progresses. Therefore, in the present invention, the first stage etching is completed when etching in the etching hole stops, and then the second stage etching is performed to further deepen and widen the etched hole while suppressing surface dissolution. It accomplishes its purpose. [Late-stage etching process] The chlorine ion concentration in the etching solution in the second-stage etching process is preferably in the range of 2 to 15% for the same reason as the first-stage etching.
A range of ~8% is optimal. The oxidizing acid added to this aqueous solution containing chlorine ions is one that suppresses dissolution of the aluminum surface by forming an anodized film on the aluminum surface through anodic polarization, and specifically includes oxalic acid, phosphoric acid, chromic acid,
Boric acid, tartaric acid, succinic acid, maleic acid, etc. can be suitably used. The second-stage etching is to proceed with etching inside the etching holes while suppressing dissolution of the aluminum foil surface.
Addition of the above acids at high concentrations is not preferred. Similarly, the addition of highly soluble sulfuric acid is also unsuitable because it also causes chemical surface dissolution and reduces the area expansion ratio.
The preferred amount of the above-mentioned acids to be added varies depending on the type of acid, but is limited to a low concentration range of 0.03 to 3%, most preferably in the range of 0.1 to 1%. If the amount added is less than 0.03%, the effect of suppressing the dissolution of the aluminum surface will be small, and if it exceeds 3%, the entire surface of the aluminum foil will be dissolved. If the temperature of the etching solution in the second stage etching is too low, it will not have the effect of widening the etching hole formed in the first stage etching, whereas if it is too high, complete dissolution will occur. Therefore, a suitable temperature range is 50 to 100°C, with a range of 60 to 70°C being particularly optimal. Generally speaking, regarding current density, it is necessary to prevent etching in the etching hole from being stopped due to generated gas in the subsequent etching process, so etching must be performed at a relatively low current density. However, the current density is 0.5A/d
If it is too low, less than m ² , the proportion of chemical reactions in the electrochemical reaction will be too high, and the effect of deepening the etching hole will be poor, leading to total dissolution.
Conversely, when the current density is set to a high current density exceeding 7 A/dm ² , the entire surface of the aluminum foil is melted, which is not preferable. Therefore, treatment should be performed within the range of 0.5 to 7 A/dm ² , and particularly the range of 2 to 5 A/dm ² is optimal. On the other hand, the range of electricity amount for post-etching is 1000
If it is ^less than 4000 coulombs/dm2, it will have little effect in making the etching hole deeper and thicker, and if it exceeds 4000 coulombs/ ^dm2 , total dissolution will occur, so within this range,
Particularly preferably, the treatment is carried out within the range of 2000 to 3000 coulombs/dm ² . Note that the above-mentioned first and second stages of etching are not necessarily carried out in a single step, but the present invention also applies when each of them is carried out in two stages, that is, when the etching process as a whole is carried out in three or more stages. Included within the scope of. As described above, this invention uses a high-purity aluminum foil containing at least one of phosphorus and arsenic, and firstly, a large number of etching holes are formed on the surface at a high density and relatively The etched hole is formed deeply, and then the inside of the etched hole is intensively made thicker and deeper by subsequent etching.As a result, the area expansion ratio can be significantly increased and the capacitance can be greatly improved, making it possible to improve the electrolytic capacitor. Not only does it enable further downsizing and weight reduction, it also eliminates the disadvantage of mechanical strength loss due to an increase in area expansion ratio, and allows cutting of aluminum foil in a series of processes such as etching, chemical conversion, and assembly. There is less risk of this, and productivity can be improved. Examples of the present invention will be shown below along with comparative examples. Sample A: Aluminum purity 99.99%, annealed aluminum foil with a thickness of 0.1 mm B: Aluminum purity 99.99%, phosphorus content
3ppm, 0.1mm thick annealed aluminum alloy foil C: Aluminum purity 99.99%, phosphorus content
20ppm, 0.1mm thick annealed aluminum alloy foil D: Aluminum purity 99.99%, arsenic content
5ppm, 0.1mm thick annealed aluminum alloy foil E: Aluminum purity 99.99%, total phosphorus and arsenic content 4.0ppm (phosphorus 1.5ppm, arsenic
2.5ppm), 0.1mm thick annealed aluminum alloy foil.
The first stage etching treatment was performed under various electrolytic conditions shown in Table 2, and the second stage etching treatment was then performed under various electrolytic conditions shown in Table 2.

【table】

【table】

【table】

[Table] After each of the etched foils obtained above was chemically converted to 380V in a boric acid solution, the capacitance and tensile strength of each sample were measured. Table the results.
Shown in 3.

【table】

【table】

[Table] As is clear from the results shown in Table 3, according to the present invention, an extremely high area ratio is obtained and the capacitance is greatly increased, while mechanical strength, especially tensile strength, is also improved. Excellent aluminum electrode foil can be obtained.

Claims (1)

[Claims] 1. Using an aluminum alloy foil having an aluminum purity of 99.9% or more and containing 0.5 to 100 wt-ppm of at least one of phosphorus and arsenic,
A pre-etching process was performed using direct current at a current density of 5 to 40 A/dm ² in an aqueous solution at 50 to 100 °C containing ~15% and 1 to 35% of an acid that produces a porous oxide film by anode polarization. This is then added to a solution containing 2-15% chloride ions and 0.03-3% oxidizing acid.
Current density 0.5-7A/d in aqueous solution at 50-100℃
1. A method for producing an aluminum alloy foil for electrolytic capacitor electrodes, which comprises performing a subsequent etching treatment using a direct current of m ² . 2. Production of aluminum alloy foil for electrolytic capacitor electrodes according to claim 1, in which an aqueous solution containing hydrochloric acid and sulfuric acid is used as an etching solution in the first stage etching, and an aqueous solution containing hydrochloric acid and oxalic acid is used as an etching solution in the second stage etching. Method.