JP4958464B2 - Aluminum foil for electrolytic capacitor electrode - Google Patents

Description

  The present invention relates to an aluminum foil for electrolytic capacitor electrodes. In particular, the present invention relates to an aluminum foil for electrolytic capacitor electrodes that can achieve a high capacitance after etching and anodizing treatment.

  Aluminum can easily increase the surface area by forming etching pits by chemical or electrochemical etching. A good quality anodic oxide film can be formed on the surface by subjecting the surface to an anodizing treatment called “chemical conversion treatment”. Moreover, since this film becomes a dielectric, the thin rolled aluminum foil is subjected to etching treatment, and the surface is subjected to chemical conversion treatment with various conversion voltages according to the use voltage to form an anodized film. Various types of capacitors that meet the requirements are manufactured.

  Etching pits formed by the etching process are drilled in a shape suitable for the level of the formation voltage according to the operating voltage.

  When used for medium- and high-voltage capacitors with a high operating voltage, it is necessary to form a thick chemical film by increasing the chemical voltage. Therefore, the etching pit is formed by direct current so that the thick chemical film does not fill the etching pit. The etching is performed by electrochemical etching, and the etching pit shape is a tunnel type.

  When used for a low-voltage capacitor with a low working voltage, the applied chemical film is not as thick as for medium-high pressure, so the pit form is fine irregularities called spongy or cauliflower, and the surface area expansion rate is medium. Larger than tunnel pit for high pressure. Such pits can be obtained by AC etching in an aqueous solution containing chlorine ions.

  In medium- and high-pressure etching, the etching process is performed in two stages: primary etching and secondary etching. In primary etching, direct current is applied to form a thin tunnel-shaped initial pit, and then in secondary etching, the diameter of the initial pit is expanded. is doing.

  Since the capacitance of the capacitor can be increased by increasing the surface area, it is necessary to generate many initial pits formed by primary etching. Moreover, the initial pits need to be uniformly distributed and distributed in an appropriate number so that the etching pits do not coalesce when the diameter is expanded by secondary etching. Since the etching pits are generated by obtaining an electrochemical starting point, first, the starting points of the initial pits must be distributed and distributed in an appropriate number of uniform manners.

  In recent years, with the trend of further miniaturization of capacitors, improvement in electrostatic capacity has been strongly demanded, and aluminum foils to which various elements are added have been proposed. For example, JP-A-60-66806 (Patent Document 1) discloses rapid quenching by dissolving aluminum containing at least one metal of 2 to 60 atomic% of titanium, zirconium, niobium, and hafnium and unavoidable impurities. An aluminum alloy electrode for an electrolytic capacitor is disclosed in which a forced solid solution alloy is formed.

  However, although the addition of these elements is suitable for forming a composite dielectric, an appropriate number of tunnel type etching pits cannot be formed, and too many initial pits are generated at the same time, so that the aluminum foil is completely dissolved. However, there is a problem that the capacitance is reduced.

  As a method for suppressing the entire surface dissolution and uniformly distributing the starting points of the initial pits in an appropriate number, an aluminum foil added with various elements has been proposed. For example, aluminum alloy foil for electrolytic capacitor electrodes in which the purity of aluminum is 99.9% or more and contains 1 to 10 ppm of one or more of Cr, Mo, W, Nb and Ta (Patent Document 2) ), The purity of the aluminum is 99.9% or more, and contains at least one element of at least one of Be, P and Ta in a total amount of 0.2 to 20 ppm, and the above-mentioned element in the surface layer part having a thickness of 1 μm from the surface The aluminum foil for electrolytic capacitor electrodes (Patent Document 3), characterized in that the total concentration of Al is set in the range of 1.5 to 500 times the content inside the foil, and Al purity: 99.9% or more Si: 2 to 50 ppm, Fe: 2 to 50 ppm, Cu: 15 to 150 ppm, Zn: 1 to 80 ppm and Pb 0.1 to 3 ppm, and among Zr and V Containing 21~100ppm one 21ppm or more and a total even without, B content is restricted to 2ppm or less, the balance being aluminum material for electrolytic capacitor electrodes, characterized in that it consists of aluminum and impurities.

However, even these methods are not sufficient for suppressing the entire surface dissolution and distributing the appropriate number of initial pit starting points uniformly, and it cannot be said that the improvement in the capacitance of the capacitor is satisfactory.
JP 60-66806 A JP-A-63-90115 JP-A-4-62824 JP 2002-97538 A

  Accordingly, the main object of the present invention is to solve the above-mentioned problems of the prior art, and to provide an aluminum foil for electrolytic capacitor electrodes for producing a capacitor capable of exhibiting a higher capacitance. It is in.

  As a result of intensive studies in view of the above problems, the present inventors have found that an aluminum foil for electrolytic capacitor electrodes having a specific chemical composition can achieve the above object, and have completed the present invention. In particular, 0.1 to 5 ppm of B and 0.1 to 3 ppm of Pb serve as starting points of initial pits having a uniform distance between etching pits, and at least one of Nb and Ta is 10 ppm or more and 10 in total. The present invention was completed on the basis of the knowledge that by containing ˜100 ppm, the etching pits proceed in a tunnel shape to suppress the entire surface dissolution.

That is, the present invention relates to the following aluminum foil for electrolytic capacitor electrodes.
1. Aluminum foil for electrolytic capacitor electrode, Al: 99.9% by mass or more, Si: 2 to 100 ppm, Fe: 2 to 100 ppm, Cu: 15 to 150 ppm, B: 0.1 to 5 ppm, Pb: 0.1 An aluminum foil for an electrolytic capacitor electrode, comprising: -3 ppm, at least one of Nb and Ta: 10 to 100 ppm, and the balance: inevitable impurities.
2. Item 2. The aluminum foil for electrolytic capacitor electrodes according to Item 1, wherein at least one of Nb and Ta is 30 to 70 ppm.
3. Item 3. The aluminum foil for electrolytic capacitor electrodes according to Item 1 or 2, wherein B is 0.1 to 2 ppm.
4). The electrolytic capacitor electrode obtained from the aluminum foil for electrolytic capacitor electrodes in any one of said 1-3.
5. Al: 99.9% by mass or more, Si: 2 to 100 ppm, Fe: 2 to 100 ppm, Cu: 15 to 150 ppm, B: 0.1 to 5 ppm, Pb: 0.1 to 3 ppm, at least one of Nb and Ta : 10-100 ppm, balance: aluminum alloy for electrolytic capacitor electrodes , characterized by comprising inevitable impurities.
6). Item 6. The aluminum alloy for electrolytic capacitor electrodes according to Item 5, wherein at least one of Nb and Ta is 30 to 70 ppm.
7). Item 7. The aluminum alloy for electrolytic capacitor electrodes according to Item 5 or 6, wherein B is 0.1 to 2 ppm .

  In the Al foil of the present invention, since specific components such as B, Nb, and Ta are controlled within a certain range, it is possible to provide an electrolytic capacitor electrode having a higher capacitance. In particular, the Al foil of the present invention is useful as a medium-high pressure etching foil.

1. Aluminum foil for electrolytic capacitor electrode The aluminum foil for electrolytic capacitor electrode of the present invention (the Al foil of the present invention) is an aluminum foil for electrolytic capacitor electrode, and Al: 99.9% by mass or more, Si: 2 to 100 ppm, Fe: It consists of 2 to 100 ppm, Cu: 15 to 150 ppm, B: 0.1 to 5 ppm, Pb: 0.1 to 3 ppm, at least one of Nb and Ta: 10 to 100 ppm, and the balance: inevitable impurities. Hereinafter, each component will be described. In the present specification, “ppm” means “mass ppm”.

<Al>
In the Al foil of the present invention, aluminum is 99.9% by mass or more, preferably 99.93% by mass or more. The aluminum foil in the present invention is made of an aluminum alloy in which such an impurity element is adjusted and a significant element is added and blended. Such an aluminum alloy (slab) is also included in the present invention.

  The Al content in the present invention includes Si, Fe, Cu, Ga, Ti, Ni, Pb, V, Zn and any additional elements (however, excluding O, N, and C) by chemical analysis or emission spectroscopy. Analyze quantitatively and define their sum as the difference minus 100. Here, O, N, and C are excluded because these elements are easily taken in in the process of preparing the analysis sample, and thus the reliability of the analysis result is low.

  Conventionally, aluminum foil for electrolytic capacitor electrodes generally used contains elements such as Fe, Si, Cu, Ti, V, and Ga as impurity elements during the smelting, refining, and melting processes of aluminum. The content of these elements can be adjusted by blending aluminum of different quality (quality). The aluminum foil finally obtained has various characteristics by adding and blending significant elements after adjusting the impurity elements in this way. The aluminum foil in the present invention is made of an aluminum alloy prepared by adjusting such impurity elements and adding significant elements.

<Si and Fe>
Si and Fe in the Al foil of the present invention are both 2 to 100 ppm, preferably 5 to 50 ppm. When at least one of Si or Fe exceeds 100 ppm, intermetallic compounds containing these are crystallized or precipitated, preventing recrystallization so that the (100) plane is parallel to the etched surface of the foil. It tends to be. Moreover, when at least one of Si or Fe is less than 2 ppm, coarse crystal grains are likely to be generated.

  In order to obtain tunnel-like etching pits extending in the thickness direction of the aluminum foil, it is desirable that the (100) plane of the aluminum fcc crystal structure is parallel to the etching plane (foil plane) of the foil. The higher the proportion of the (100) plane parallel to, the higher the capacitance can be obtained.

  Such an aluminum foil is re-crystallized by heat treatment at a temperature of 300 to 650 ° C. in a vacuum or an inert gas atmosphere in a final foil rolling process in which the foil is rolled to a thickness of about 100 μm. The (100) surface of the structure is aligned so as to be parallel to the etching surface (rolled surface). At that time, the (100) plane parallel to the etched surface of the foil is desirably 95% or more. In order to maintain and promote such effects, the Si and Fe contents are set in the above range.

  Further, in the present invention, if there are coarse crystal grains having a diameter exceeding 1 mm in the recrystallized structure, the capacitance of the foil is lowered. Therefore, a recrystallized structure composed of fine crystal grains having a diameter of about 0.5 mm or less is preferable. .

<Cu>
Cu in the Al foil of the present invention is usually contained in an amount of about 15 to 150 ppm, preferably 25 to 100 ppm. Cu is an effective component when the diameter is expanded by secondary etching, but if the content is less than 15 ppm, the effect of expanding the initial pit in the secondary etching is reduced. Also, if it exceeds 150 ppm, the dissolution during secondary etching becomes severe, the tunnel shape after the initial pit enlargement collapses, and the etching surface cannot be greatly enlarged as a ratio to the projected area, resulting in improved capacitance Cannot be expected.

<B and Pb>
In the Al foil of the present invention, B is usually contained in an amount of about 0.1 to 5 ppm, preferably 0.1 to 2 ppm. Further, Pb is usually contained in an amount of about 0.1 to 3 ppm, preferably 0.3 to 1.5 ppm. When the contents of B and Pb are each less than 0.1 ppm, the starting point of the initial pit is not sufficient, and an aluminum foil having a high capacitance cannot be obtained. Further, when the contents of B and Pb exceed 5 ppm and 3 ppm, respectively, the initial pit start point becomes excessive, the tunnel shape after the initial pit enlargement collapses, and the etching surface cannot be enlarged as a ratio to the projected area. As a result, the capacitance cannot be improved.

  B and Pb are concentrated on the surface of the aluminum foil by the influence of heat received during the manufacturing process of the aluminum foil. That is, B and Pb contained in the material of the foil rolling are diffused and concentrated on the foil surface by a high temperature annealing process, particularly a process of 470 ° C. or higher, which is the final process of the foil rolling. When B and Pb are present on the surface in a concentrated manner, the solubility of the foil surface is improved and it becomes the starting point of the initial pit in the primary etching. In addition, the coexistence of B and Pb makes it possible to uniformly distribute and distribute the initial pit starting points in an appropriate number, thereby contributing to an improvement in capacitance.

<At least one of Nb and Ta>
In the Al foil of the present invention, at least one of Nb and Ta is usually 10 to 100 ppm, preferably 21 to 80 ppm, more preferably 30 to 70 ppm, and most preferably 50 to 70 ppm. These components are effective elements when the initial pits are advanced in a tunnel shape from the starting point in the primary etching. When the content is less than 10 ppm, the initial pit start point becomes excessive, the tunnel shape after the initial pit enlargement collapses, and the etching surface cannot be greatly enlarged as a ratio of projected area, and an aluminum foil having a high capacitance is obtained. I can't get it. In addition, when the content exceeds 100 ppm, dissolution during secondary etching becomes severe, the tunnel shape after the initial pit enlargement collapses, the etching area cannot be enlarged as a ratio of projected area, and aluminum having a high capacitance A foil cannot be obtained.

<Other ingredients>
Other impurities such as Mn, Mg, Cr, Zn and V may be 100 ppm or less.

<Al foil thickness>
The thickness of the aluminum foil is not limited, but is generally preferably 50 to 200 μm, particularly preferably 70 to 150 μm. Even if the surface area is the same, as the foil thickness increases, the capacitance per unit weight of the aluminum foil may decrease. A foil thickness exceeding 200 μm is contrary to the recent demand for miniaturization of electrolytic capacitors. On the other hand, if the foil thickness is less than 50 μm, the strength after etching may be lowered before it can be used.

2. Method for Producing Aluminum Foil for Electrolytic Capacitor Electrode The aluminum foil of the present invention is produced according to a known method for producing aluminum foil for electrolytic capacitor electrodes, regardless of whether it is a hard foil or a soft foil, except that the composition is set to the above composition. can do.

  For example, a molten metal having the above predetermined composition is prepared, and an ingot obtained by casting the molten metal is homogenized at 450 to 660 ° C., then subjected to hot rolling and cold rolling, and then 300 to 650 ° C. It can be obtained by annealing. If necessary, intermediate annealing at 150 to 400 ° C. may be performed during the cold rolling.

  When manufacturing an electrolytic capacitor electrode from the Al foil of the present invention, it may be carried out according to a known etching method, chemical conversion treatment, or the like. For example, after performing primary etching and secondary etching, an electrolytic capacitor electrode can be more suitably manufactured by performing chemical conversion treatment. Each processing condition may be as follows, for example, but is not limited thereto.

Primary etching The etching solution used in the primary etching process is not limited, and a known etching solution such as an acid aqueous solution containing hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, or the like can be used. The concentration of the etching solution is not particularly limited, but is usually set to 1 to 8 mol / L, preferably 3 to 5 mol / L. The temperature of the etching solution is not particularly limited, but a preferable solution temperature is 65 to 85 ° C. If the liquid temperature is high, the reaction is promoted, which is preferable. However, if the temperature is too high, the reaction is too fast and the foil surface is so melted that it becomes difficult to form uniform initial tunnel pits.

Primary etching is usually performed in direct current (DC). In that case, the current density is generally preferably about 0.1 to 0.7 A / cm ² . The treatment time is usually about 30 seconds to 3 minutes.

Secondary etching Secondary etching is mainly performed to enlarge the diameter of etching pits drilled by primary etching.

  The etching solution used in the secondary etching process is not limited, and for example, a known etching solution such as an acid aqueous solution containing hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, or the like can be used. The concentration of the etching solution is not particularly limited, but is usually set to 0.1 to 3 mol / L, preferably 0.2 to 2 mol / L. The temperature of the etching solution is not particularly limited, but a preferable solution temperature is 70 to 90 ° C. If the liquid temperature is high, the reaction is promoted, which is preferable. However, if the temperature is too high, the reaction is too fast and it is difficult to increase the etching pit diameter.

Secondary etching is usually performed by direct current (DC) or chemical dissolution. In general, the current density in the case of DC etching is preferably about 0.1 to 0.3 A / cm ² . The treatment time is usually about 2 to 20 minutes. Moreover, the processing time at the time of chemical dissolution is suitably about 5 to 30 minutes.

In the chemical conversion treatment, an anodic oxide film is formed on an aluminum foil whose surface area is increased by forming pits by etching treatment. Specifically, a chemical conversion treatment using the aluminum foil as an anode is performed to form an anodized film.

  The chemical conversion treatment may be performed under known conditions. For example, a buffer solution such as ammonium borate, ammonium phosphate, or organic acid ammonium (for example, ammonium adipate) is used as an electrolytic solution, and a voltage of about 100 to 1000 V is applied in one step or multiple steps depending on the use of the capacitor. (That is, a dielectric film) is formed.

  In this invention, you may perform the process by an acid or an alkali liquid for the surface adjustment etc. of aluminum foil prior to a primary etching process as needed. This treatment itself can be performed according to a known method.

  Examples and Comparative Examples are shown below to further clarify the features of the present invention. However, the scope of the present invention is not limited to these examples.

  In addition, the characteristic of the sample obtained by the Example and the comparative example was measured as follows.

<Al foil composition>
The composition of the Al foil was performed using an emission spectroscopic analyzer. However, the composition of Pb was performed by wet chemical analysis. Further, since the contents of elements other than those shown in Table 1 were stable and very small, the Al content (%) was a value obtained by subtracting the total value of the indicated element contents from 100%.

<Capacitance>
The capacitance of the sample was measured with an aqueous ammonium borate solution (3 g / L) after being subjected to an etching treatment under the following conditions, subjected to a chemical conversion treatment at 350 V in an aqueous boric acid solution (50 g / L).

Etching conditions
Primary etching etching solution: Mixed solution of hydrochloric acid and sulfuric acid (hydrochloric acid concentration: 1 mol / L, sulfuric acid concentration: 3 mol / L, 80 ° C.)
Electrolysis: DC 500 mA / cm ² × 1 min
Secondary etching etching solution: nitric acid solution (nitric acid concentration: 1 mol / L, 75 ° C.)
Electrolysis: DC 100 mA / cm ² × 5 minutes Examples 1 to 14 and Comparative Examples 1 to 8
The mold casting slab having the composition shown in Table 1 was held at a temperature of 600 ° C. for 10 hours and homogenized, and then hot rolled and cold rolled to give a thin plate having a thickness of 130 μm. This thin plate is maintained at a temperature of 260 ° C. for 5 hours, subjected to intermediate annealing, and further cold-rolled to obtain an aluminum foil having a thickness of 110 μm, and then annealed by holding it in an Ar gas atmosphere at 530 ° C. for 5 hours. This produced a sample for evaluation.

  Table 1 shows the capacitance of each sample and dissolution loss during etching. These are indicated by indices (relative values) when the value obtained with the aluminum foil of Comparative Example 1 is taken as 100.

  As is clear from the results in Table 1, Examples 5, 7, 10, 12 and the like in which at least one of Nb and Ta is in the range of 50 to 70 ppm in total achieve a high value of capacitance 110 or more. I understand that I can do it. In particular, it can be seen that Example 10, Example 11 or Example 12 in which B is in the range of 0.1 to 0.5 ppm has a higher capacitance.

Claims (7)

Aluminum foil for electrolytic capacitor electrode, Al: 99.9% by mass or more, Si: 2 to 100 ppm, Fe: 2 to 100 ppm, Cu: 15 to 150 ppm, B: 0.1 to 5 ppm, Pb: 0.1 An aluminum foil for an electrolytic capacitor electrode, comprising: -3 ppm, at least one of Nb and Ta: 10 to 100 ppm, and the balance: inevitable impurities. The aluminum foil for electrolytic capacitor electrodes according to claim 1, wherein at least one of Nb and Ta is 30 to 70 ppm. The aluminum foil for electrolytic capacitor electrodes according to claim 1 or 2, wherein B is 0.1 to 2 ppm. The electrolytic capacitor electrode obtained from the aluminum foil for electrolytic capacitor electrodes in any one of Claims 1-3. Al: 99.9% by mass or more, Si: 2 to 100 ppm, Fe: 2 to 100 ppm, Cu: 15 to 150 ppm, B: 0.1 to 5 ppm, Pb: 0.1 to 3 ppm, at least one of Nb and Ta : 10-100 ppm, balance: aluminum alloy for electrolytic capacitor electrodes , characterized by comprising inevitable impurities. The aluminum alloy for electrolytic capacitor electrodes according to claim 5, wherein at least one of Nb and Ta is 30 to 70 ppm. The aluminum alloy for electrolytic capacitor electrodes according to claim 5 or 6, wherein B is 0.1 to 2 ppm.