JP2007113085A - Aluminum foil for electrolytic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make obtainable of a high roughening surface ratio of an aluminum foil for electrolytic capacitor with a non-electrolytic etching. <P>SOLUTION: This aluminum foil has a composition composed, by mass, of 5-40 ppm Si, 5-40 ppm Fe, 0.1-3 ppm Pb and 20-200 ppm total content as additional elements of one or more among the elements selected from Mn, Ni, Sn, Ag, Pt, Au and the balance ≥99.9% Al with inevitable impurities, and the oxidized film thickness is 20-60 Å. An ionic strength ratio at 0.5 μm depth from the surface is made to ≥1.5, in the case that the ionic strength of the above additional elements at 1 μm depth position in the aluminum foil is defined as 1, and ionic strength ratio at 0.1 μm depth is made to ≥10, and the ionic strength ratio at the 0.3 μm depth is made to ≥2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an aluminum foil for electrolytic capacitor electrodes used for electrodes of electrolytic capacitors.

Conventionally, the etching foil for electrolytic capacitors has an aluminum purity of 99.9% or more, Si: 5 to 20 ppm, Fe: 5 to 20 ppm, Cu: 10 to 80 ppm, Pb: 0.1 to 3 ppm, and other trace impurities 1 to Made of 100ppm, manufactured as an aluminum foil that has undergone hot rolling, cold rolling, intermediate annealing, additional rolling, annealing at 500 ° C or more for 3 hours or more, and having a cubic rate of 95% or more. Yes.
The aluminum foil is further subjected to electrolytic etching in a strong acid solution to generate corrosion holes (hereinafter referred to as pits), and then the electrolytic solution or chemical dissolution in the acid solution is used to adjust the pit diameter according to the voltage in the formation of the next step. It has expanded to size.
As a feature of high-purity aluminum foil, since passivation proceeds in an acid solution, chemical solubility is low, and therefore, electrolytic etching is considered indispensable. In order to obtain the required number of pits by electrolytic etching, an amount of electricity of 40 to 60 C / cm ² is required, and a large amount of electricity is consumed to obtain this.
For reducing the amount of electricity described above, it is effective to improve the etching property of the aluminum foil. For example, Patent Document 1 proposes disposing various elements on the surface of the oxide film or on the interface between the oxide film and the foil substrate. In Patent Document 1, it is pointed out that the element arranged on the surface of the foil acts as a base point of the etching pit, so that it is important to arrange it in the extreme surface layer portion.
JP-A-4-213810

Usually, with the progress of the etching reaction, the aluminum foil surface is missing, and 0.1 to 0.5 μm of the surface layer is removed. Therefore, although the element arrange | positioned at the extreme surface layer part as shown by patent document 1 can contribute to the reactivity in the initial stage, it cannot contribute over the whole etching reaction.
Further, when the purity of the aluminum foil is lowered to about 99%, chemical solubility is promoted by the impurity element in the aluminum foil. However, due to the decrease in aluminum purity, the uniformity of crystal orientation is lost and the growth of etching pits is no longer unidirectional, so that only surface dissolution proceeds and normal etching pits cannot be obtained. In order to keep the cubic rate at 95%, an aluminum purity of 99.9% or more is necessary, and it is difficult to adjust the chemical solubility by the aluminum purity.

  The present invention has been made against the background of the above circumstances, and significantly reduces the chemical reactivity of high-purity aluminum foil, and provides a foil capable of generating pits without using electricity, thereby reducing costs in etching. The purpose is to improve productivity.

  In the generation of etching pits mainly composed of chemical dissolution, which is the object of the present invention, it is necessary that the chemical reaction generated on the surface of the aluminum foil proceeds continuously. It is necessary to continue at least 0.5 μm deep inside the foil. The inventors have found that a specific element is contained in an amount that does not decrease the aluminum purity, that is, 1000 ppm or less, and can be concentrated on the surface of the aluminum foil by heat treatment, and the present invention has been completed.

  That is, the invention of the aluminum foil for electrolytic capacitors of the present invention is an aluminum foil for electrolytic capacitors to be used for etching, and in terms of mass ratio, Si: 5 to 40 ppm, Fe: 5 to 40 ppm, Pb: 0.1 It contains 3 ppm, and among elements selected from Mn, Ni, Sn, Ag, Pt, and Au, one or two or more elements are added as additive elements in a total amount of 20 to 200 ppm, and the balance is 99.9% or more An ionic strength ratio at a depth of 0.1 μm having a composition comprising Al and inevitable impurities, an oxide film thickness of 20 to 60 mm, and an ionic strength of the additive element at a depth of 1 μm of the aluminum foil as 1. Has a concentration gradient in which the ion intensity ratio at a depth of 10 or more and 0.3 μm is 2 or more and the ion intensity ratio at a depth of 0.5 μm is 1.5 or more.

  Below, the effect | action by each component of this invention and the reason which limited each component are demonstrated. In addition, all the component content in the following is mass ratio.

Si: 5 to 40 ppm, Fe: 5 to 40 ppm
Si and Fe combine with Al to appropriately generate precipitates, suppress coarsening of recrystallized grains, and promote preferential growth of Cube grains. However, if it is less than 5 ppm, the purification cost becomes high, which is unsuitable industrially. On the other hand, in the case where each exceeds 40 ppm, the total amount of precipitates becomes too large to control the preferential growth of Cube grains, so that a high cubic crystal ratio cannot be obtained. For this reason, the content of Si and Fe is set within the above range. A desirable lower limit is 10 ppm for both Si and Fe, and a desirable upper limit is 20 ppm for both Si and Fe.

Pb: 0.1 to 3 ppm
Pb is an element that makes surface dissolution uniform in etching. However, if it is less than 0.1 ppm, the effect cannot be expected, and if it exceeds 3 ppm, the solubility becomes too high and excessive dissolution occurs. Therefore, the content of Pb is defined above. A desirable lower limit is 0.2 ppm, and a desirable upper limit is 1 ppm.

One or more of Mn, Ni, Sn, Ag, Pt, Au: Total amount 20 to 200 ppm
Since these additive elements and bulk aluminum cause a local battery reaction, pits can be generated even without electrolysis. In order to generate etching pits from the foil surface layer, it is necessary to contain an appropriate amount of these substances, specifically 20 to 200 ppm in total, and to concentrate on the aluminum foil surface by heat treatment. When the total amount is less than 20 ppm, the above-mentioned effect cannot be obtained sufficiently, and electroless etching becomes difficult. On the other hand, if the content exceeds 200 ppm, the pit generation becomes excessive and the pit generation efficiency deteriorates due to the pit coupling. For the same reason, it is desirable to set the lower limit to 50 ppm and the upper limit to 180 ppm.

Oxide film thickness (20-60mm)
In the aluminum foil immediately before being subjected to the etching treatment, it is necessary that an oxide film having an appropriate thickness is formed on the surface. When the thickness of the oxide film is less than 20 mm, the roughening rate is reduced due to excessive surface dissolution. When the thickness exceeds 60 mm, the surface is dissolved locally and the roughening rate is decreased. Set. The oxide film thickness can be measured by, for example, X-ray photoelectron analysis (ESCA). In addition, a measuring apparatus structure and a measurement procedure are not specifically limited as this invention, It can carry out by a conventional method.

Ion intensity ratio:
0.1 μm depth: 10 or more, 0.3 μm depth: 2 or more, 0.5 μm depth: 1.5 or more The additive element is concentrated in the surface layer portion and has the concentration gradient described above. Is desirable. By having a higher concentration on the surface side, pit generation is effectively promoted, and pits are effectively grown in the depth direction to improve the roughening rate. In addition, when the said additional element is 2 or more types, the said ionic strength ratio should just be satisfy | filled with the total amount.

Aluminum purity: 99.9% or more If the purity is less than 99.9%, the uniformity of crystal orientation is lost and normal etching pits cannot be obtained. An aluminum purity of 99.9% or more is necessary to ensure the uniformity of crystal orientation and keep the cubic ratio at 95% or more.

  As explained above, the aluminum foil for electrolytic capacitors of the present invention is an aluminum foil for electrolytic capacitors to be used for etching, and has a mass ratio of Si: 5 to 40 ppm, Fe: 5 to 40 ppm, Pb: 0.00. 1 to 3 ppm, and among elements selected from Mn, Ni, Sn, Ag, Pt, and Au, one or more elements are added as additive elements, and the total content is 20 to 200 ppm, the balance being 99.9% It has a composition comprising the above Al and inevitable impurities, has an oxide film thickness of 20 to 60 mm, and has an ionic strength of the additive element at a depth of 1 μm of the aluminum foil as 1 and a depth of 0.5 μm from the surface. The ionic strength ratio is 1.5 or more, the ionic strength ratio at a depth of 0.1 μm is 10 or more, and the ionic strength ratio at a depth of 0.3 μm is 2 or more. Pits in grayed is efficiently generated, it is possible to obtain good roughening rate. This makes it possible to reduce costs and improve productivity when manufacturing electrolytic capacitors.

A high-purity aluminum material prepared to be a component of the present invention with a purity of 99.9% or more is prepared. The aluminum material preferably has a purity of 99.95% or more.
The aluminum material can be obtained by a conventional method, and the production method is not particularly limited in the present invention. For example, a hot-rolled slab obtained by semi-continuous casting can be used, or a high-purity aluminum material obtained by continuous casting can be used. For example, a sheet material having a thickness of about several mm is formed by the hot rolling or continuous casting rolling. This sheet material is cold-rolled to obtain an aluminum alloy foil of about several tens of μm to 100 μm. In addition, degreasing may be appropriately added during the cold rolling or after the end of the cold rolling, and intermediate annealing may be appropriately added during the cold rolling.
After the final cold rolling, a final annealing heat treatment is performed. The heating conditions for the final annealing are important for concentrating the above-described additive elements in the surface layer portion. For example, a reducing atmosphere using 500 to 580 ° C. × 3 to 24 hr, H ₂ , Ar, N ₂ or the like By heating in an inert atmosphere, an aluminum alloy foil having an oxide film with an average thickness of 20 to 60 mm can be obtained. In a reducing atmosphere, a mixed gas obtained by mixing a reducing gas such as H ₂ with an inert gas or a small amount of oxygen can be used. It is desirable that the cubic crystal ratio is 95% or more. The said additional element concentrates on a surface layer part by the said annealing. If annealing is performed under vacuum, an oxide film is not properly formed on the surface, and good etching becomes difficult during etching.

The aluminum foil obtained through the above steps is then subjected to an etching process. The etching step can be performed by electroless etching using an electrolytic solution mainly composed of hydrochloric acid or an electrolytic solution not containing hydrochloric acid. However, the present invention may employ electrolytic etching, and in that case, a good roughening rate can be obtained.
The etching process can be performed by a surface layer portion removing process, an etching pit generating process, and an etching pit hole diameter expanding process. The surface layer portion removing step is performed by dissolving the surface layer portion including the oxide film. After removing the surface layer portion, an etching pit generation step is performed for generating etching pits on the surface of the aluminum foil. After the etching pit generation process, an etching pit hole diameter expanding process is performed.
In the etching process, pits are formed with high density even in electroless process, and a high roughening rate is obtained. After this foil is subjected to chemical conversion treatment to obtain the necessary piezoelectric resistance, a capacitor having a high capacitance can be obtained by incorporating it as an electrode in an electrolytic capacitor by a conventional method.

  The present invention is preferably used as an anode of a medium-high voltage electrolytic capacitor. However, the present invention is not limited to this, and can be used for a capacitor having a lower formation voltage. It can also be used as a cathode material.

Ingots having the components shown in the table were prepared and subjected to a soaking treatment at 500 ° C. or higher for 30 minutes or longer, followed by hot rolling at a processing rate of 95 to 99%. At that time, the finishing temperature was 250 to 400 ° C. After hot rolling, cold rolling of 95% or more was performed to prepare a sample having a foil thickness of 110 μm. During cold rolling, intermediate annealing was performed as necessary.
These foils were annealed in an atmosphere of Ar, N ₂ , H ₂ or the like at the temperatures and times shown in Table 2 to produce foils having a cubic crystal ratio of 95% or more. Samples with different concentration gradients were obtained by changing the temperature and time during annealing. The oxide film thickness was measured by ESCA (x-ray photoelectron spectroscopy).
The concentration gradient of the element was determined by detecting the ion intensity at each depth position using SIMS (secondary ion mass measuring device).

  These aluminum foils were immersed in a 3 mol / l sulfuric acid solution at 40 ° C. to remove the oxide film. After removing the film, it was washed with water and immersed in a mixed acid solution of 70 ° C., 1 mol / l hydrochloric acid + 3 mol / l sulfuric acid for 60 seconds to generate etching pits. After the pit was generated, it was washed with water and immersed in a 3 mol / l sulfuric acid solution at 75 ° C. for 600 sec to enlarge the pit diameter. After expanding the pit diameter, it was washed with ion-exchanged water and dried.

  The obtained etching foil was subjected to chemical conversion at 300 V with a 10 wt% boric acid solution to evaluate the capacitance, and relative evaluation was made assuming that Example 1 was 100%.

As in Examples 1 to 9, in the case of the foil added with the additive element, it can be seen that etching pits are generated by chemical dissolution and a high capacitance is obtained. The change in the depth direction of the ionic strength ratio of Example 1 is shown in FIG. As shown in the figure. With respect to a depth position of 1 μm from the surface, the ionic strength ratio at a depth of 0.1 μm is 10 or more, the ionic strength ratio at a depth of 0.3 μm is 2 or more, and the ionic strength ratio at a depth of 0.5 μm is 1. The concentration of the additive element in the surface layer is excellent.
When the additive element of Comparative Example 1 is not added, etching pits are not generated, and the electrostatic capacity is remarkably reduced. In addition, when the concentration gradient does not continue to the depth of 0.5 μm, etching pits are generated, but the number is insufficient, so the value is generally low.

It is a graph which shows the depth position of the aluminum foil in one Example of this invention, and the ionic strength ratio of an addition element.

Claims (1)

  An aluminum foil for electrolytic capacitors to be used for etching, containing, by mass ratio, Si: 5 to 40 ppm, Fe: 5 to 40 ppm, Pb: 0.1 to 3 ppm, and Mn, Ni, Sn, Ag, Among elements selected from Pt and Au, one or two or more elements as additive elements are contained in a total amount of 20 to 200 ppm, with the balance being 99.9% or more of Al and inevitable impurities, and the oxide film thickness Is 20 to 60 mm, and the ionic strength ratio at the depth of 0.1 μm is 10 or more and the ionic strength ratio at the depth of 0.3 μm, where the ionic strength of the additive element at the depth of 1 μm of the aluminum foil is 1. An aluminum foil for electrolytic capacitors, wherein the aluminum foil has a concentration gradient in which the ionic strength ratio at a depth of 2 or more and 0.5 μm is 1.5 or more.

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