JP2008266746A - Aluminum foil for electrolytic capacitor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a surface roughening ratio in application of aluminum foil for an electrolytic capacitor of a high working voltage by effectively performing diameter expansion when etching the aluminum foil for the electrolytic capacitor. <P>SOLUTION: The aluminum foil consists of the composition containing 10 to 30 ppm Si, 10 to 20 ppm Fe, 0.3 to 3 ppm Pb, 10 to 70 ppm Cu, and 10 to 50 ppm Ni, and the balance ≥99.9% Al and inevitable impurities, and the Ni concentration distribution maintains ≥10 times the average content over the entire part in the average content of 0.1 μm depth from the surface layer, ≤0.5 times the average content over the entire part in the average content of 1 to ≤5 μm depth from the surface layer, and ≥80% of the average content over the entire part at 20 μm depth. The Ni concentration distribution is obtained by heating up the aluminum foil of the composition in an inert gas or gaseous hydrogen or an atmosphere of a gaseous mixture composed thereof, and heating up the aluminum foil at a heating up rate 30 to 100°C/hour in a process of at least 300 to 450°C and subjecting the aluminum foil to final annealing of a holding time 2 to 24 hours. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an aluminum foil for an electrolytic capacitor used for etching for use in an electrode of an electrolytic capacitor, and a method for manufacturing the same.

Medium and high pressure aluminum foils used for medium and high voltage electrolytic capacitors are used with direct current electrolysis to open countless pit-shaped holes to increase the surface area. In order to uniformly generate the etching pits, a foil having a cube orientation occupation ratio of 95% or more is used.
In order to increase the cube orientation occupancy, usually 4N purity aluminum is used, and the components are adjusted to Si 5-30 ppm, Fe 5-20 ppm, Cu 10-70 ppm, Pb 0.2-3.0 ppm, hot rolling, cold rolling, intermediate A foil rolled to a thickness of 90 to 130 μm through annealing and cold rolling is used after annealing at 450 ° C. or more for 3 hours or more.

This aluminum foil is used by etching to enlarge the surface area. Etching is performed in acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, or mixed acids. Since high-purity aluminum has strong acid resistance, it is difficult to generate etching pits only by chemical dissolution. Therefore, direct current electrolytic etching is performed. After generating the etching pits, electrolytic treatment in an acid solution or chemical dissolution treatment is performed as a pit diameter enlargement treatment. As the working voltage of the capacitor increases, a larger pit diameter is required, and a foil with high etching efficiency is required.
Patent Document 1 proposes an aluminum foil for an electrolytic capacitor intended to make it easy to obtain a cubic crystal ratio by containing Cu 10 to 100 ppm and Ni 10 to 500 ppm, and as a result, to improve etching properties.
JP-A 61-255911

  However, according to the Example of the said patent document 1, the final annealing is performed by vacuum annealing. Since vacuum annealing has a low thermal conductivity, the temperature rising rate of the aluminum foil is remarkably slow. For this reason, Ni concentrates to the foil surface layer part, and there is a problem that the effect of increasing the solubility inside the foil, which is the main purpose of this patent, cannot be obtained.

  The present invention has been made against the background of the above circumstances, and for electrolytic capacitors that improve the etching efficiency by effectively forming large-diameter pits during etching by increasing the solubility on the foil surface and inside the foil. An object is to provide an aluminum foil and a method for producing the same.

  That is, the aluminum foil for electrolytic capacitors of this invention contains Si: 10-30ppm, Fe: 10-20ppm, Pb: 0.3-3ppm, Cu: 10-70ppm, Ni: 10-50ppm by mass ratio. The balance is 99.9% or more of Al and inevitable impurities. In the Ni concentration distribution, the average content from the surface layer to the depth of 0.1 μm is 10% of the total average content (Ni: 10 to 50 ppm). The average content at a depth of 1 to 5 μm is 0.5 times or less of the total average content, and at a depth of 20 μm or more, 80% or more of the total average content is maintained. It is characterized by that.

  Moreover, invention of the manufacturing method of the aluminum foil for electrolytic capacitors of this invention is Si: 10-30ppm, Fe: 10-20ppm, Pb: 0.3-3ppm, Cu: 10-70ppm, Ni: 10 by mass ratio. An aluminum foil containing ˜50 ppm and having the balance of 99.9% or more of Al and unavoidable impurities in an atmosphere of inert gas, hydrogen gas or a mixed gas thereof at least at a temperature of 300 to 450 ° C. The temperature is increased at a temperature increase rate of 30 to 100 ° C./hour, and the final annealing is performed at a holding temperature of 500 to 580 ° C. and a holding time of 2 to 24 hours.

The inventors of the present invention have found that the chemical solubility of the aluminum foil can be enhanced by adding a specific element and controlling the annealing conditions to appropriately distribute the element. Specifically, the concentration of Ni can be appropriately controlled by adding Ni and controlling the rate of temperature rise during annealing.
When Ni is annealed, it concentrates on the foil surface layer and produces Al—Ni-based precipitates. Since Al—Ni-based precipitates are more noble than bulk Al, a local battery can be generated and solubility can be increased. Further, since Ni concentration occurs in the portion of the foil surface layer of several μm, the added Ni exists inside the foil. This Ni increases the solubility in the aluminum. As a result, in the etching pit diameter expansion process, the pit diameter expansion is promoted, and a larger pit diameter can be obtained. In order to concentrate Ni on the surface and to make it exist in the inside of the foil on an added amount basis, the rate of temperature rise and surface oxide film control are effective.

Below, each condition prescribed | regulated by this invention is demonstrated.
(Aluminum foil component)
Aluminum purity of 99.9% or more If the purity of the aluminum foil is less than 99.9%, the cubic crystal ratio decreases, which is not desirable. Inevitable impurities include components specific to bullion. Even if three-layer metal or segregated metal is used, there is no problem as long as 99.9% or more is secured as the aluminum purity after adjusting Si, Fe, Pb, Cu, and Ni.

Si: 10-30 ppm
When Si is less than 10 ppm, the purification cost increases, which is not desirable industrially. On the other hand, if it exceeds 30 ppm, the cubic rate decreases, which is not desirable. For this reason, Si content is defined to the said range. Preferably, the lower limit is 10 ppm and the upper limit is 20 ppm.

Fe: 10-20ppm
When Fe is less than 10 ppm, the purification cost increases, which is not industrially desirable. On the other hand, if it exceeds 20 ppm, the cubic rate decreases, which is not desirable. For this reason, Fe content is defined to the said range. Preferably, the lower limit is 10 ppm and the upper limit is 15 ppm.

Pb: 0.3 to 3 ppm
Pb is an element that makes the oxide film brittle and improves the etching property. However, if it is less than 0.3 ppm, the effect cannot be expected, while if it exceeds 3 ppm, excessive dissolution of the foil surface layer is caused. Therefore, the Pb content is set within the above range. Preferably the lower limit is 0.3 ppm and the upper limit is 1.5 ppm.

Cu: 10 to 70 ppm
Cu is an element that enhances the solubility in the foil. However, if it is less than 10 ppm, the combined effect with Ni is reduced and the chemical solubility is lowered. For this reason, the effect of expanding the pit diameter cannot be expected. On the other hand, if it exceeds 70 ppm, the cubic rate decreases, which is not desirable. Therefore, the Cu content is set within the above range. Preferably the lower limit is 20 ppm and the upper limit is 40 ppm.

Ni: 10-50ppm
Ni is an element that causes surface concentration and produces Al—Ni-based precipitates to increase the solubility of the foil surface and to increase the solubility inside the foil by remaining inside the foil. When it is less than 10 ppm, improvement in solubility inside the foil cannot be expected. On the other hand, when it exceeds 50 ppm, the solubility of the foil surface layer becomes strong, and the control by etching becomes difficult. For this reason, Ni content is defined to the said range. Preferably the lower limit is 20 ppm and the upper limit is 40 ppm.

Temperature increase rate at 300 to 450 ° C .: 30 to 100 ° C./hour Since Ni concentration occurs from 300 ° C. or higher, at a temperature increase rate of 30 to 100 ° C./hour at least between the annealing temperatures of 300 to 450 ° C. Need to be maintained. When the rate of temperature rise is less than 30 ° C./hour, Ni inside the foil also moves to the surface layer and concentrates, so that the effect of expanding the pit diameter cannot be obtained. On the other hand, when the temperature exceeds 100 ° C./hour, the surface oxide film grows before the Ni is concentrated and prevents the Ni from being concentrated, resulting in a decrease in chemical solubility. Therefore, the temperature rising rate at least at an annealing temperature of 300 to 450 ° C. is set in the above range. In the temperature range exceeding 450 ° C., the rate of temperature rise can be reduced as the temperature approaches the holding temperature. However, when the holding temperature is high, the temperature rising rate can be maintained above 450 ° C. For the same reason as described above, it is desirable that the lower limit of the heating rate is 40 / hour and the upper limit is 80 ° C./hour.

Holding temperature: 500 to 580 ° C., holding time 2 to 24 hours By holding the aluminum foil in the above temperature range and annealing, a high cubic crystal ratio (for example, 95% or more) can be obtained. If the holding temperature is less than 500 ° C. or the holding time is less than 2 hours, it is difficult to obtain a sufficient cubic rate. On the other hand, when the temperature exceeds 580 ° C. for more than 24 hours, excessive film formation occurs and the etching property decreases. In addition, the foil comes into close contact with each other, resulting in poor peeling.

Surface oxide film thickness 20-100mm
It is desirable to control the surface oxide film after annealing to 20 to 100%. When the thickness is less than 20%, the corrosion resistance of the foil is lowered, the storage stability of the annealed foil is deteriorated, and abnormal causes such as surface oxidation are caused. On the other hand, when the thickness exceeds 100 mm, the uniformity is reduced during etching, causing a reduction in capacity. It is preferably 40 to 60 mm. The film thickness is a value obtained by ESCA (X-ray photoelectron spectroscopy).

Annealing atmosphere In order to make the temperature rising rate and oxide film thickness within the above ranges, it is necessary to appropriately select the atmosphere during annealing.
In vacuum annealing, the heat conduction during annealing is significantly deteriorated, so that the rate of temperature rise is reduced. Furthermore, since the oxide film on the foil surface layer becomes thin, it is not preferable. In the case of atmospheric annealing, the oxide film on the foil surface layer becomes thick and the etching property is lowered, which is not preferable. In the case of an inert gas atmosphere such as Ar or N ₂ , an appropriate oxide film can be formed by controlling the dew point and the oxygen partial pressure. It is necessary to consider the shape and quantity of the foil. Industrially, when annealing a coiled aluminum foil in units of Ton, it is desirable to perform with hydrogen gas. This is because the thermal conductivity is high, so that a sufficient annealing rate can be obtained, and since it is a reducing atmosphere, the growth of the oxide film can also be suppressed. However, the selection of appropriate conditions for the inert gas can also achieve the targets of the annealing rate and the oxide film thickness, and is not excluded. In vacuum annealing and atmospheric annealing, the targets of the rate of temperature rise and the thickness of the oxide film cannot be achieved. The atmosphere gas may be a mixture of an inert gas and hydrogen gas.

Ni concentration distribution The existence state of Ni after annealing needs to be in the state shown in FIG. That is, it is necessary to concentrate 10 times or more of the average content of the entire aluminum foil up to the depth of 0.1 μm of the foil surface layer. The term “10 times or more” means that the average content from the foil surface layer portion to the depth of 0.1 μm is 10 times or more of the total average content. Below this, the reactivity of the foil surface layer decreases, so the number of pits decreases and the capacity decreases. On the other hand, at a depth of 20 μm or more, it is necessary to substantially maintain 80% or more of the average content of the entire aluminum foil. This is to increase the solubility in the foil and facilitate the enlargement of the pit diameter.
Further, Ni inside the foil is not moved, and Ni in the vicinity of the surface layer is concentrated on the surface, so that a Ni-deficient region occurs between 1 to 5 μm deep. When the surface concentration is 10 times or more of the addition amount, the average content is ½ or less of the average content of the entire aluminum foil in the depth of 1 to 5 μm.

  As described above, according to the aluminum foil for electrolytic capacitors of the present invention, by mass ratio, Si: 10 to 30 ppm, Fe: 10 to 20 ppm, Pb: 0.3 to 3 ppm, Cu: 10 to 70 ppm, Ni: It contains 10 to 50 ppm, the balance is 99.9% or more of Al and inevitable impurities, and in the Ni concentration distribution, the average content from the surface layer to a depth of 0.1 μm is the overall average content (Ni: 10 to 50 ppm), the average content at a depth of 1 to 5 μm is 0.5 times or less of the total average content, and at a depth of 20 μm or more, 80% of the total average content Since the above is maintained, the solubility on the foil surface and inside the foil can be obtained satisfactorily, and the pits having an enlarged diameter can be efficiently generated and the surface area can be increased during etching.

  Moreover, according to the manufacturing method of the aluminum foil for electrolytic capacitors of this invention, by mass ratio, Si: 10-30ppm, Fe: 10-20ppm, Pb: 0.3-3ppm, Cu: 10-70ppm, Ni: 10 An aluminum foil containing ˜50 ppm and having the balance of 99.9% or more of Al and unavoidable impurities in an atmosphere of inert gas, hydrogen gas or a mixed gas thereof at least at a temperature of 300 to 450 ° C. The temperature is increased at a rate of temperature increase of 30 to 100 ° C./hour, and the final annealing is performed at a holding temperature of 500 to 580 ° C. and a holding time of 2 to 24 hours. An appropriate amount of Ni is present in each case, thereby making it possible to reliably obtain the action of the aluminum foil for 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, and a high-purity aluminum material obtained by continuous casting can also 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 particularly important for concentrating Ni in the surface layer portion among the above-described additive elements, and for leaving the Ni inside, preferably a reducing atmosphere using H ₂ or the like In an inert atmosphere such as Ar, N ₂ or a mixed gas atmosphere thereof, heating is performed at a temperature increase rate of 30 to 100 ° C./hour between at least 300 to 450 ° C., and 500 to 580 ° C. × 2 to 24 An aluminum alloy foil having an oxide film with an average thickness of 20 to 100 mm can be obtained by heating for a period of time. In a reducing atmosphere, it is possible to use a mixed gas obtained by mixing a reducing gas such as H ₂ with an inert gas or a small amount of oxygen. 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. When annealing is performed under vacuum, an oxide film is not properly formed on the surface, and good etching becomes difficult during etching.

  The final annealing particularly controls the concentration distribution of Ni in the depth direction, and the average Ni concentration from the surface layer to a depth of 0.1 μm is 10 times or more the average concentration of Ni in the entire aluminum foil. Moreover, in the depth of 1-5 micrometers, Ni density | concentration reduces by concentration to the surface layer side, and is 0.5 times or less of the average density | concentration of Ni of the whole aluminum foil. At a depth of 20 μm or more, the average concentration of Ni in the entire aluminum foil is substantially maintained at 80% or more.

The aluminum foil obtained through the above steps is then subjected to an etching process. The etching step can be performed by electrolytic etching using an electrolytic solution mainly composed of hydrochloric acid. In the present invention, the type of the electrolytic solution is not particularly limited. Further, in the present invention, since Al—Ni-based precipitates are present on the surface layer, electroless etching is also possible.
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 the surface layer portion is removed, an etching pit generation step for generating etching pits on the aluminum foil surface is performed. After the etching pit generation process, an etching pit hole diameter expanding process is performed. This foil is subjected to a chemical conversion treatment to obtain a required withstand voltage, and then a capacitor having a high capacitance is 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.

After adjusting the composition shown in Table 1 (the balance 99.99% Al and other inevitable impurities) using 4N purity aluminum ingot, an aluminum slab was prepared by a semi-continuous casting method. Hot rolling was performed after soaking at 580 ° C. for 2 hours or more. At that time, the finishing temperature was 230 ° C. to 350 ° C., and the processing rate was 90% or more. After hot rolling, cold rolling was performed. At that time, intermediate annealing at 150 ° C. to 300 ° C. for 2 to 24 hours was performed, and further cold working of 10 to 20% was performed to obtain a 120 μm aluminum foil. In addition, the intermediate annealing was performed at a stage where the processing rate in cold rolling was 95% or more.
The obtained aluminum foil was annealed under the conditions shown in Table 2. The rate of temperature increase is a value between 300 and 450 ° C. Then, the surface layer part was dissolved by changing the dissolution depth by changing the immersion time in 1 M / L NaOH, 45 ° C. solution, and the remaining aluminum foil was analyzed by ICP. The average Ni content up to a depth of 0.1 μm, the average Ni content at a depth of 1 to 5 μm, and the Ni content at a depth of 20 μm or more were calculated, and the results are shown in Table 2.

In addition, pit generation etching was performed by applying a direct current of 300 mA / cm ² for 120 seconds in 1M hydrochloric acid + 3M sulfuric acid at 80 ° C. for the specimen not dissolved. After performing pit generation etching, the pit diameter was expanded by immersion in the same solution for 20 minutes. The obtained etching foil was electropolished and the surface layer was removed by 20 μm, and then the pit shape was observed by SEM. The SEM image was analyzed and the pit diameter was calculated. The results are shown in Table 2. Further, the etching foil was formed by applying a voltage of 300 V in 85 g of a boric acid solution of 100 g / l, and then the capacitance was measured. Example 1 was set to 100%, and the others were compared relative to each other.

It is a figure which shows Ni concentration distribution in the depth direction of the aluminum foil for electrolytic capacitors of this invention.

Claims (2)

  Si: 10 to 30 ppm, Fe: 10 to 20 ppm, Pb: 0.3 to 3 ppm, Cu: 10 to 70 ppm, Ni: 10 to 50 ppm, with the balance being 99.9% or more of Al and inevitable It has a composition consisting of impurities, and in the Ni concentration distribution, the average content from the surface layer to the depth of 0.1 μm is 10 times or more of the total average content (Ni: 10 to 50 ppm), and at a depth of 1 to 5 μm. The aluminum foil for electrolytic capacitors, wherein the average content is 0.5 times or less of the total average content, and 80% or more of the total average content is maintained at a depth of 20 μm or more.   Si: 10 to 30 ppm, Fe: 10 to 20 ppm, Pb: 0.3 to 3 ppm, Cu: 10 to 70 ppm, Ni: 10 to 50 ppm, with the balance being 99.9% or more of Al and inevitable An aluminum foil having a composition composed of impurities is heated at a temperature rising rate of 30 to 100 ° C./hour in a process of at least 300 to 450 ° C. in an atmosphere of inert gas, hydrogen gas or a mixed gas thereof, and a holding temperature of 500 The manufacturing method of the aluminum foil for electrolytic capacitors characterized by performing final annealing in -580 degreeC and holding time 2-24 hours.

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